I am not disputing you but I think it is impossible to go just back a version barring some kind of major malfunction. Even if you factory reset after an update, it should stay on that update. The only way to revert to a previous version would be to use Odin back and reflash the stock or maybe flash an old nandroid backup. I would take your phones in to Sprint if you are sure they have gone back because there's no normal way that should happen.