Fix #8584: Vehicles with shared orders getting invalid or unexpected start dates

src/lang/english.txt

@@ -4468,7 +4468,7 @@ STR_TIMETABLE_STATUS_NOT_STARTED                                :{BLACK}This tim
 STR_TIMETABLE_STATUS_START_AT                                   :{BLACK}This timetable will start at {STRING1}
 
 STR_TIMETABLE_STARTING_DATE                                     :{BLACK}Start date
-STR_TIMETABLE_STARTING_DATE_TOOLTIP                             :{BLACK}Select a date as starting point of this timetable. Ctrl+Click sets the starting point of this timetable and distributes all vehicles sharing this order evenly based on their relative order, if the order is completely timetabled
+STR_TIMETABLE_STARTING_DATE_TOOLTIP                             :{BLACK}Select a date as starting point of this timetable. Ctrl+Click distributes all vehicles sharing this order evenly from the given date based on their relative order, if the order is completely timetabled
 
 STR_TIMETABLE_CHANGE_TIME                                       :{BLACK}Change Time
 STR_TIMETABLE_WAIT_TIME_TOOLTIP                                 :{BLACK}Change the amount of time that the highlighted order should take

src/timetable_cmd.cpp

@@ -249,11 +249,14 @@ CommandCost CmdSetTimetableStart(DoCommandFlag flags, VehicleID veh_id, bool tim
 	CommandCost ret = CheckOwnership(v->owner);
 	if (ret.Failed()) return ret;
 
+	int total_duration = v->orders->GetTimetableTotalDuration();
+
 	/* Don't let a timetable start more than 15 years into the future or 1 year in the past. */
 	if (start_date < 0 || start_date > MAX_DAY) return CMD_ERROR;
 	if (start_date - _date > 15 * DAYS_IN_LEAP_YEAR) return CMD_ERROR;
 	if (_date - start_date > DAYS_IN_LEAP_YEAR) return CMD_ERROR;
 	if (timetable_all && !v->orders->IsCompleteTimetable()) return CMD_ERROR;
+	if (timetable_all && start_date + total_duration / DAY_TICKS > MAX_DAY) return CMD_ERROR;
 
 	if (flags & DC_EXEC) {
 		std::vector<Vehicle *> vehs;
@@ -266,14 +269,13 @@ CommandCost CmdSetTimetableStart(DoCommandFlag flags, VehicleID veh_id, bool tim
 			vehs.push_back(v);
 		}
 
-		int total_duration = v->orders->GetTimetableTotalDuration();
 		int num_vehs = (uint)vehs.size();
 
 		if (num_vehs >= 2) {
 			std::sort(vehs.begin(), vehs.end(), &VehicleTimetableSorter);
 		}
 
-		int idx = vehs.begin() - std::find(vehs.begin(), vehs.end(), v);
+		int idx = 0;
 
 		for (Vehicle *w : vehs) {