diff --git a/frontend/apps/reader/modules/readertypography.lua b/frontend/apps/reader/modules/readertypography.lua
index 7e263a9f6..5ad82e922 100644
--- a/frontend/apps/reader/modules/readertypography.lua
+++ b/frontend/apps/reader/modules/readertypography.lua
@@ -12,10 +12,14 @@ local C_ = _.pgettext
 local T = require("ffi/util").template
 local Screen = Device.screen
 
+local ReaderTypography = InputContainer:new{}
+
 -- This is used to migrate old hyph settings, and to show the currently
 -- used hyph dict language in the hyphenation menu.
 -- It will be completed with info from the LANGUAGES table below.
-local HYPH_DICT_NAME_TO_LANG_NAME_TAG = {
+-- NOTE: Actual migration is handled in ui/data/onetime_migration,
+--       which is why this hash is public.
+ReaderTypography.HYPH_DICT_NAME_TO_LANG_NAME_TAG = {
     ["@none"]                = { "@none",           "en" },
     ["@softhyphens"]         = { "@softhyphens",    "en" },
     ["@algorithm"]           = { "@algorithm",      "en" },
@@ -93,7 +97,7 @@ local LANGUAGES = {
     { "zu",               {"zul"},   "H   ",   _("Zulu"),                   "Zulu.pattern" },
 }
 
-local DEFAULT_LANG_TAG = "en-US" -- English_US.pattern is loaded by default in crengine
+ReaderTypography.DEFAULT_LANG_TAG = "en-US" -- English_US.pattern is loaded by default in crengine
 
 local LANG_TAG_TO_LANG_NAME = {}
 local LANG_ALIAS_TO_LANG_TAG = {}
@@ -106,12 +110,10 @@ for __, v in ipairs(LANGUAGES) do
         end
     end
     if hyph_filename then
-        HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_filename] = { lang_name, lang_tag }
+        ReaderTypography.HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_filename] = { lang_name, lang_tag }
     end
 end
 
-local ReaderTypography = InputContainer:new{}
-
 function ReaderTypography:init()
     self.menu_table = {}
     self.language_submenu = {}
@@ -124,44 +126,6 @@ function ReaderTypography:init()
     self.hyph_force_algorithmic = false
     self.floating_punctuation = 0
 
-    -- Migrate old readerhyphenation settings (but keep them in case one
-    -- go back to a previous version)
-    if G_reader_settings:hasNot("text_lang_default") and G_reader_settings:hasNot("text_lang_fallback") then
-        local g_text_lang_set = false
-        local hyph_alg_default = G_reader_settings:readSetting("hyph_alg_default")
-        if hyph_alg_default then
-            local dict_info = HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_alg_default]
-            if dict_info then
-                G_reader_settings:saveSetting("text_lang_default", dict_info[2])
-                g_text_lang_set = true
-                -- Tweak the other settings if the default hyph algo happens
-                -- to be one of these:
-                if hyph_alg_default == "@none" then
-                    G_reader_settings:makeFalse("hyphenation")
-                elseif hyph_alg_default == "@softhyphens" then
-                    G_reader_settings:makeTrue("hyph_soft_hyphens_only")
-                elseif hyph_alg_default == "@algorithm" then
-                    G_reader_settings:makeTrue("hyph_force_algorithmic")
-                end
-            end
-        end
-        local hyph_alg_fallback = G_reader_settings:readSetting("hyph_alg_fallback")
-        if not g_text_lang_set and hyph_alg_fallback then
-            local dict_info = HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_alg_fallback]
-            if dict_info then
-                G_reader_settings:saveSetting("text_lang_fallback", dict_info[2])
-                g_text_lang_set = true
-                -- We can't really tweak other settings if the hyph algo fallback
-                -- happens to be @none, @softhyphens, @algortihm...
-            end
-        end
-        if not g_text_lang_set then
-            -- If nothing migrated, set the fallback to DEFAULT_LANG_TAG,
-            -- as we'll always have one of text_lang_default/_fallback set.
-            G_reader_settings:saveSetting("text_lang_fallback", DEFAULT_LANG_TAG)
-        end
-    end
-
     local info_text = _([[
 Some languages have specific typographic rules: these include hyphenation, line breaking rules, and language specific glyph variants.
 KOReader will choose one according to the language tag from the book's metadata, but you can select another one.
@@ -639,7 +603,7 @@ end
 
 function ReaderTypography:getCurrentDefaultHyphDictLanguage()
     local hyph_dict_name = self.ui.document:getTextMainLangDefaultHyphDictionary()
-    local dict_info = HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_dict_name]
+    local dict_info = self.HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_dict_name]
     if dict_info then
         hyph_dict_name = dict_info[1]
     else -- shouldn't happen
@@ -703,7 +667,7 @@ function ReaderTypography:onReadSettings(config)
     -- Migrate old readerhyphenation setting, if one was set
     if config:hasNot("text_lang") and config:has("hyph_alg") then
         local hyph_alg = config:readSetting("hyph_alg")
-        local dict_info = HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_alg]
+        local dict_info = self.HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_alg]
         if dict_info then
             config:saveSetting("text_lang", dict_info[2])
             -- Set the other settings if the default hyph algo happens
@@ -792,7 +756,7 @@ function ReaderTypography:onReadSettings(config)
     else
         self.allow_doc_lang_tag_override = true
         -- None decided, use default (shouldn't be reached)
-        self.text_lang_tag = DEFAULT_LANG_TAG
+        self.text_lang_tag = self.DEFAULT_LANG_TAG
         logger.dbg("Typography lang: no lang set, using", self.text_lang_tag)
     end
     self.ui.document:setTextMainLang(self.text_lang_tag)
diff --git a/frontend/cache.lua b/frontend/cache.lua
index e7add0d23..5f075cf72 100644
--- a/frontend/cache.lua
+++ b/frontend/cache.lua
@@ -39,12 +39,6 @@ end
 
 local cache_path = DataStorage:getDataDir() .. "/cache/"
 
--- NOTE: Before 2021.04, fontlist used to squat our folder, needlessly polluting our state tracking.
-os.remove(cache_path .. "/fontinfo.dat")
--- Ditto for Calibre
-os.remove(cache_path .. "/calibre-libraries.lua")
-os.remove(cache_path .. "/calibre-books.dat")
-
 --[[
 -- return a snapshot of disk cached items for subsequent check
 --]]
@@ -160,7 +154,7 @@ function Cache:serialize()
     -- calculate disk cache size
     local cached_size = 0
     local sorted_caches = {}
-    for _,file in pairs(self.cached) do
+    for _, file in pairs(self.cached) do
         table.insert(sorted_caches, {file=file, time=lfs.attributes(file, "access")})
         cached_size = cached_size + (lfs.attributes(file, "size") or 0)
     end
@@ -203,4 +197,9 @@ function Cache:clear()
     self.current_memsize = 0
 end
 
+-- Refresh the disk snapshot (mainly used by ui/data/onetime_migration)
+function Cache:refreshSnapshot()
+    self.cached = getDiskCache()
+end
+
 return Cache
diff --git a/frontend/ui/data/onetime_migration.lua b/frontend/ui/data/onetime_migration.lua
new file mode 100644
index 000000000..a7b61c9bb
--- /dev/null
+++ b/frontend/ui/data/onetime_migration.lua
@@ -0,0 +1,202 @@
+--[[
+Centralizes any and all one time migration concerns.
+--]]
+
+local DataStorage = require("datastorage")
+local lfs = require("libs/libkoreader-lfs")
+local logger = require("logger")
+
+-- Date at which the last migration snippet was added
+local CURRENT_MIGRATION_DATE = 20210413
+
+-- Retrieve the date of the previous migration, if any
+local last_migration_date = G_reader_settings:readSetting("last_migration_date", 0)
+
+-- If there's nothing new to migrate since the last time, we're done.
+if last_migration_date == CURRENT_MIGRATION_DATE then
+    return
+end
+
+-- Keep this in rough chronological order, with a reference to the PR that implemented the change.
+
+-- Global settings, https://github.com/koreader/koreader/pull/4945 & https://github.com/koreader/koreader/pull/5655
+-- Limit the check to the most recent update. ReaderUI calls this one unconditionally to update docsettings, too.
+if last_migration_date < 20191129 then
+    logger.info("Performing one-time migration for 20191129")
+
+    local SettingsMigration = require("ui/data/settings_migration")
+    SettingsMigration:migrateSettings(G_reader_settings)
+end
+
+-- ReaderTypography, https://github.com/koreader/koreader/pull/6072
+if last_migration_date < 20200421 then
+    logger.info("Performing one-time migration for 20200421")
+
+    local ReaderTypography = require("apps/reader/modules/readertypography")
+    -- Migrate old readerhyphenation settings
+    -- (but keep them in case one goes back to a previous version)
+    if G_reader_settings:hasNot("text_lang_default") and G_reader_settings:hasNot("text_lang_fallback") then
+        local g_text_lang_set = false
+        local hyph_alg_default = G_reader_settings:readSetting("hyph_alg_default")
+        if hyph_alg_default then
+            local dict_info = ReaderTypography.HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_alg_default]
+            if dict_info then
+                G_reader_settings:saveSetting("text_lang_default", dict_info[2])
+                g_text_lang_set = true
+                -- Tweak the other settings if the default hyph algo happens to be one of these:
+                if hyph_alg_default == "@none" then
+                    G_reader_settings:makeFalse("hyphenation")
+                elseif hyph_alg_default == "@softhyphens" then
+                    G_reader_settings:makeTrue("hyph_soft_hyphens_only")
+                elseif hyph_alg_default == "@algorithm" then
+                    G_reader_settings:makeTrue("hyph_force_algorithmic")
+                end
+            end
+        end
+        local hyph_alg_fallback = G_reader_settings:readSetting("hyph_alg_fallback")
+        if not g_text_lang_set and hyph_alg_fallback then
+            local dict_info = ReaderTypography.HYPH_DICT_NAME_TO_LANG_NAME_TAG[hyph_alg_fallback]
+            if dict_info then
+                G_reader_settings:saveSetting("text_lang_fallback", dict_info[2])
+                g_text_lang_set = true
+                -- We can't really tweak other settings if the hyph algo fallback happens to be
+                -- @none, @softhyphens, @algortihm...
+            end
+        end
+        if not g_text_lang_set then
+            -- If nothing migrated, set the fallback to DEFAULT_LANG_TAG,
+            -- as we'll always have one of text_lang_default/_fallback set.
+            G_reader_settings:saveSetting("text_lang_fallback", ReaderTypography.DEFAULT_LANG_TAG)
+        end
+    end
+end
+
+-- NOTE: ReaderRolling, on the other hand, does some lower-level things @ onReadSettings tied to CRe that would be much harder to factor out.
+--       https://github.com/koreader/koreader/pull/1930
+-- NOTE: The Gestures plugin also handles its settings migration on its own, but deals with it sanely.
+
+-- ScreenSaver, https://github.com/koreader/koreader/pull/7371
+if last_migration_date < 20210306 then
+    logger.info("Performing one-time migration for 20210306 (1/2)")
+
+    -- Migrate settings from 2021.02 or older.
+    if G_reader_settings:readSetting("screensaver_type") == "message" then
+        G_reader_settings:saveSetting("screensaver_type", "disable")
+        G_reader_settings:makeTrue("screensaver_show_message")
+    end
+    if G_reader_settings:has("screensaver_no_background") then
+        if G_reader_settings:isTrue("screensaver_no_background") then
+            G_reader_settings:saveSetting("screensaver_background", "none")
+        end
+        G_reader_settings:delSetting("screensaver_no_background")
+    end
+    if G_reader_settings:has("screensaver_white_background") then
+        if G_reader_settings:isTrue("screensaver_white_background") then
+            G_reader_settings:saveSetting("screensaver_background", "white")
+        end
+        G_reader_settings:delSetting("screensaver_white_background")
+    end
+end
+
+-- OPDS, same as above
+if last_migration_date < 20210306 then
+    logger.info("Performing one-time migration for 20210306 (2/2)")
+
+    local opds_servers = G_reader_settings:readSetting("opds_servers")
+    if opds_servers then
+        -- Update deprecated URLs & remove deprecated entries
+        for i = #opds_servers, 1, -1 do
+            local server = opds_servers[i]
+
+            if server.url == "http://bookserver.archive.org/catalog/" then
+                server.url = "https://bookserver.archive.org"
+            elseif server.url == "http://m.gutenberg.org/ebooks.opds/?format=opds" then
+                server.url = "https://m.gutenberg.org/ebooks.opds/?format=opds"
+            elseif server.url == "http://www.feedbooks.com/publicdomain/catalog.atom" then
+                server.url = "https://catalog.feedbooks.com/catalog/public_domain.atom"
+            end
+
+            if server.title == "Gallica [Fr] [Searchable]" or server.title == "Project Gutenberg [Searchable]" then
+                table.remove(opds_servers, i)
+            end
+        end
+        G_reader_settings:saveSetting("opds_servers", opds_servers)
+    end
+end
+
+-- Statistics, https://github.com/koreader/koreader/pull/7471
+if last_migration_date < 20210330 then
+    logger.info("Performing one-time migration for 20210330")
+
+    -- c.f., PluginLoader
+    local package_path = package.path
+    package.path = string.format("%s/?.lua;%s", "plugins/statistics.koplugin", package_path)
+    local ok, ReaderStatistics = pcall(dofile, "plugins/statistics.koplugin/main.lua")
+    package.path = package_path
+    if not ok or not ReaderStatistics then
+        logger.warn("Error when loading plugins/statistics.koplugin/main.lua:", ReaderStatistics)
+    else
+        local settings = G_reader_settings:readSetting("statistics", ReaderStatistics.default_settings)
+        -- Handle a snafu in 2021.03 that could lead to an empty settings table on fresh installs.
+        for k, v in pairs(ReaderStatistics.default_settings) do
+            if settings[k] == nil then
+                settings[k] = v
+            end
+        end
+        G_reader_settings:saveSetting("statistics", settings)
+    end
+end
+
+-- ScreenSaver, https://github.com/koreader/koreader/pull/7496
+if last_migration_date < 20210404 then
+    logger.info("Performing one-time migration for 20210404")
+
+    -- Migrate settings from 2021.03 or older.
+    if G_reader_settings:has("screensaver_background") then
+        G_reader_settings:saveSetting("screensaver_img_background", G_reader_settings:readSetting("screensaver_background"))
+        G_reader_settings:delSetting("screensaver_background")
+    end
+end
+
+-- Fontlist, cache migration, https://github.com/koreader/koreader/pull/7524
+if last_migration_date < 20210409 then
+    logger.info("Performing one-time migration for 20210409")
+
+    -- NOTE: Before 2021.04, fontlist used to squat our folder, needlessly polluting our state tracking.
+    local cache_path = DataStorage:getDataDir() .. "/cache"
+    local new_path = cache_path .. "/fontlist"
+    lfs.mkdir(new_path)
+    local ok, err = os.rename(cache_path .. "/fontinfo.dat", new_path .. "/fontinfo.dat")
+    if not ok then
+       logger.warn("os.rename:", err)
+    end
+
+    -- Make sure Cache gets the memo
+    local Cache = require("cache")
+    Cache:refreshSnapshot()
+end
+
+-- Calibre, cache migration, https://github.com/koreader/koreader/pull/7528
+if last_migration_date < 20210412 then
+    logger.info("Performing one-time migration for 20210412")
+
+    -- Ditto for Calibre
+    local cache_path = DataStorage:getDataDir() .. "/cache"
+    local new_path = cache_path .. "/calibre"
+    lfs.mkdir(new_path)
+    local ok, err = os.rename(cache_path .. "/calibre-libraries.lua", new_path .. "/libraries.lua")
+    if not ok then
+       logger.warn("os.rename:", err)
+    end
+    ok, err = os.rename(cache_path .. "/calibre-books.dat", new_path .. "/books.dat")
+    if not ok then
+       logger.warn("os.rename:", err)
+    end
+
+    -- Make sure Cache gets the memo
+    local Cache = require("cache")
+    Cache:refreshSnapshot()
+end
+
+-- We're done, store the current migration date
+G_reader_settings:saveSetting("last_migration_date", CURRENT_MIGRATION_DATE)
diff --git a/frontend/ui/data/settings_migration.lua b/frontend/ui/data/settings_migration.lua
index b4bbf9827..d36444259 100644
--- a/frontend/ui/data/settings_migration.lua
+++ b/frontend/ui/data/settings_migration.lua
@@ -24,7 +24,7 @@ function SettingsMigration:migrateSettings(config)
         return
     end
 
-    -- Fine-grained CRe margins (#4945)
+    -- Fine-grained CRe margins (https://github.com/koreader/koreader/pull/4945)
     if config:has("copt_page_margins") then
         local old_margins = config:readSetting("copt_page_margins")
         logger.info("Migrating old", cfg_class, "CRe margin settings: L", old_margins[1], "T", old_margins[2], "R", old_margins[3], "B", old_margins[4])
@@ -36,7 +36,7 @@ function SettingsMigration:migrateSettings(config)
         config:delSetting("copt_page_margins")
     end
 
-    -- Space condensing to Word spacing
+    -- Space condensing to Word spacing (https://github.com/koreader/koreader/pull/5655)
     -- From a single number (space condensing) to a table of 2 numbers ({space width scale, space condensing}).
     -- Be conservative and don't change space width scale: use 100%
     if config:hasNot("copt_word_spacing") and config:has("copt_space_condensing") then
diff --git a/frontend/ui/screensaver.lua b/frontend/ui/screensaver.lua
index a6d9c0bcf..6177916ea 100644
--- a/frontend/ui/screensaver.lua
+++ b/frontend/ui/screensaver.lua
@@ -23,29 +23,6 @@ local _ = require("gettext")
 local Screen = Device.screen
 local T = require("ffi/util").template
 
--- Migrate settings from 2021.02 or older.
-if G_reader_settings:readSetting("screensaver_type") == "message" then
-    G_reader_settings:saveSetting("screensaver_type", "disable")
-    G_reader_settings:makeTrue("screensaver_show_message")
-end
-if G_reader_settings:has("screensaver_no_background") then
-    if G_reader_settings:isTrue("screensaver_no_background") then
-        G_reader_settings:saveSetting("screensaver_background", "none")
-    end
-    G_reader_settings:delSetting("screensaver_no_background")
-end
-if G_reader_settings:has("screensaver_white_background") then
-    if G_reader_settings:isTrue("screensaver_white_background") then
-        G_reader_settings:saveSetting("screensaver_background", "white")
-    end
-    G_reader_settings:delSetting("screensaver_white_background")
-end
--- Migrate settings from 2021.03 or older.
-if G_reader_settings:has("screensaver_background") then
-    G_reader_settings:saveSetting("screensaver_img_background", G_reader_settings:readSetting("screensaver_background"))
-    G_reader_settings:delSetting("screensaver_background")
-end
-
 -- Default settings
 if G_reader_settings:hasNot("screensaver_show_message") then
     G_reader_settings:makeFalse("screensaver_show_message")
diff --git a/frontend/version.lua b/frontend/version.lua
index f07597d62..702949c2f 100644
--- a/frontend/version.lua
+++ b/frontend/version.lua
@@ -67,4 +67,22 @@ function Version:getShortVersion()
     return self.short
 end
 
+--- Returns the release date of the current version of KOReader, YYYYmmdd, in UTC.
+--- Technically closer to the build date, but close enough where official builds are concerned ;).
+-- @treturn int date
+function Version:getBuildDate()
+    if not self.date then
+        local lfs = require("libs/libkoreader-lfs")
+        local mtime = lfs.attributes("git-rev", "modification")
+        if mtime then
+            local ts = os.date("!%Y%m%d", mtime)
+            self.date = tonumber(ts) or 0
+        else
+            -- No git-rev file?
+            self.date = 0
+        end
+    end
+    return self.date
+end
+
 return Version
diff --git a/plugins/opds.koplugin/opdsbrowser.lua b/plugins/opds.koplugin/opdsbrowser.lua
index 3e737f9c0..c36b97905 100644
--- a/plugins/opds.koplugin/opdsbrowser.lua
+++ b/plugins/opds.koplugin/opdsbrowser.lua
@@ -80,13 +80,6 @@ local OPDSBrowser = Menu:extend{
 }
 
 function OPDSBrowser:init()
-    -- Update deprecated URLs
-    for _, server in ipairs(self.opds_servers) do
-        if server.url == "http://bookserver.archive.org/catalog/" then
-            server.url = "https://bookserver.archive.org"
-        end
-    end
-
     self.item_table = self:genItemTableFromRoot()
     self.catalog_title = nil
     Menu.init(self) -- call parent's init()
diff --git a/plugins/statistics.koplugin/main.lua b/plugins/statistics.koplugin/main.lua
index 9dfdfdd0b..d2f9d208a 100644
--- a/plugins/statistics.koplugin/main.lua
+++ b/plugins/statistics.koplugin/main.lua
@@ -125,6 +125,19 @@ function ReaderStatistics:isDocless()
     return self.ui == nil or self.ui.document == nil
 end
 
+-- NOTE: This is used in a migration script by ui/data/onetime_migration,
+--       which is why it's public.
+ReaderStatistics.default_settings = {
+    min_sec = DEFAULT_MIN_READ_SEC,
+    max_sec = DEFAULT_MAX_READ_SEC,
+    is_enabled = true,
+    convert_to_db = nil,
+    calendar_start_day_of_week = DEFAULT_CALENDAR_START_DAY_OF_WEEK,
+    calendar_nb_book_spans = DEFAULT_CALENDAR_NB_BOOK_SPANS,
+    calendar_show_histogram = true,
+    calendar_browse_future_months = false,
+}
+
 function ReaderStatistics:init()
     if not self:isDocless() and self.ui.document.is_pic then
         return
@@ -132,23 +145,7 @@ function ReaderStatistics:init()
     self.start_current_period = os.time()
     self:resetVolatileStats()
 
-    local default_settings = {
-        min_sec = DEFAULT_MIN_READ_SEC,
-        max_sec = DEFAULT_MAX_READ_SEC,
-        is_enabled = true,
-        convert_to_db = nil,
-        calendar_start_day_of_week = DEFAULT_CALENDAR_START_DAY_OF_WEEK,
-        calendar_nb_book_spans = DEFAULT_CALENDAR_NB_BOOK_SPANS,
-        calendar_show_histogram = true,
-        calendar_browse_future_months = false,
-    }
-    self.settings = G_reader_settings:readSetting("statistics", default_settings)
-    -- Handle a snafu in 2021.03 that could lead to an empty settings table on fresh installs.
-    for k, v in pairs(default_settings) do
-        if self.settings[k] == nil then
-            self.settings[k] = v
-        end
-    end
+    self.settings = G_reader_settings:readSetting("statistics", self.default_settings)
 
     self.ui.menu:registerToMainMenu(self)
     self:checkInitDatabase()
diff --git a/reader.lua b/reader.lua
index 0f97da2bb..88b2fe225 100755
--- a/reader.lua
+++ b/reader.lua
@@ -172,14 +172,13 @@ if Device:hasEinkScreen() then
     end
 end
 
--- Handle global settings migration
-local SettingsMigration = require("ui/data/settings_migration")
-SettingsMigration:migrateSettings(G_reader_settings)
-
 -- Document renderers canvas
 local CanvasContext = require("document/canvascontext")
 CanvasContext:init(Device)
 
+-- Handle one time migration stuff (settings, deprecation, ...) in case of an upgrade...
+require("ui/data/onetime_migration")
+
 -- Touch screen (this may display some widget, on first install on Kobo Touch,
 -- so have it done after CanvasContext:init() but before Bidi.setup() to not
 -- have mirroring mess x/y probing).