Originally Posted by
sethb
I've seen them selling upgrades when all Medallions have cleared. They started with the high fare classes, then offered to everybody when they still had seats left.
I have never seen this done starting at the top and descending by fare class, but it is common for them to require a minimum fare class to be eligible (sorry, I don't recall what that fare class was... it's been a long time since I have seen this done).