Check the reservation on the app. It'll lose the QR code if they pull the car in the reservations system and will likely be noticable before a notification is sent to you if you check regularly.I'll be in the 532 car on 9/30. Haven't seen any emails altering that yet, & (fingers crossed) hope I don't see any.
If the QR code is still there, the car is still in the reservations system. That doesn't mean it'll stay there, though.
If I were you, I'd call and see if you can get moved to the 31 car anyway.