I’m too lazy to read the thread right now, but if it helps, I have multiple 3DS’s and I’ve never had an issue playing my games on any of them. My saves function normally on all the 3DS systems, despite them all having different update versions of the game. The save file is 100% on the cartridge and the save should not be deleted.
they’re probably just deleting the “title” to prevent any corruption issues. It would probably cause some issue if there were two versions of the game on the ds.
Can’t really answer what exactly will be deleted, but I can place my bets it’s just the title and update data