Agree its rare
Agree its rare to get bumped up, but I have had it happen in the last few years a few times (2 or 3 I think), especially to tourist heavy destinations like LAS. Had a coach seat, and when I checked in was bumped up. I was not going to use upgrades as with Seat 9E I have all the leg room I need, and even though I'm going to LAS, its an early flight, so I may lay off the booze!
First class seat availability was based on seat map on aa.com which I realize can be inaccurate.
Question is really around, IF it where to happen, would the people at the airport looking to free up space and bump someone up, look at my reservation and say "he's already checked in, lets not move that guy at it complicates things when he gets to the gate."
Not a big deal, as I'm not desperate for the upgrade, just more of a curiousity question.