I'm a GM. Booked a Full Y fare ATL-MCO, March 31-April 1. The return flight upgraded me at time of booking, but the outbound Fl. 434 at 5:55pm wouldn't upgrade me, despite showing some 21 seats open in First.

I called in, the agent didn't really know why, said "give it some time." I tweeted DeltaAssist and they said "In this case, there aren't upgrade seats set aside for that flight. Had there been, you probably would've gotten it like on the return."

What does that mean? I figured "at time of booking" means if there is an open first class seat and you are a medallion booking a full Y fare, you get it?