Originally Posted by Zorak

Yes.



Theoretically revenue management may make additional upgrade inventory available between the opening of the check-in window and when the gate takes control; if so then however many people may get upgraded according to the usual priority rules (which may include people who have not checked in yet and therefore do not appear on the visible upgrade list).

Although that does happen occasionally, unless there are a ton of seats it is more likely that no one will be upgraded until whenever the gate agent processes them, typically some time inside of an hour before departure, before boarding begins.