I had an unusual upgrade experience this week while flying from IAD to DFW. I was second on the upgrade list for an M fare, with one passenger ahead of me. However, 12 hours before departure, I received a notification that I had been upgraded to FC, while the passenger who was originally ranked first remained in that position. The only difference was that I had already checked in, whereas the passenger at number one had not. Does anyone know why the upgrade algo skipped me the passenger at number one? Do you need to be checked-in to clear the upgrade list at T-24?