Originally Posted by metallo

I had a feeling that's what you meant, but if Y is oversold and one J seat is open, such that they're selling the last seat as Y instead of J (which is certainly possible), that seat would go to whoever is #1 on the upgrade list. Y fares used to go to the top of that list within each status group, but that's no longer the case (assuming I'm understanding your comment properly).

On the other hand, the above discussion may be moot if the seat is open on the map because someone bought J and simply never selected a seat, which isn't uncommon with travel agent bookings, for example.