Originally Posted by VPescado
What I've always wondered about is what happens when you cann't support the upgrade, but Y is full.
I bet it depends on the timeframe and the agent.
If it is at the gate and boarding is commencing, then I bet they just op-up you.
If it is at check-in, they probably pull you from the DM list which means the next person on the DM list will get your F/C seat and you get their Y seat. If nobody is on the DM list, then I imagine they will op-up you.