Originally Posted by kenn0223

Since auto check-in is set to happen by default it's likely that a lot of passengers are all check-in at T-24. I have no idea how they sort, but would guess an easy way would be by ticket number (but it could be any number of things).

You realize that sequence number is the very last tie-breaker for upgrades right and even then its only for the gate upgrades. These days, IME, there are usually <2 seats unallocated by the time T-30m arrives (since the auto-upgrade runs until then); often it is 0. The only time the sequence number would matter is if you're tied at both status and fare code for the last remaining seat.