Thank you, that makes a lot more sense then (contrast to United which shows both of those groups of people on the upgrade list).

In that case, is it true that there should never be a list that has both a) available seats and b) passengers on the list? (i.e. if there were available seats, they would be given to passengers in priority order, until either there were no seats left, or no passengers left on the list)? That seems to match what I'm typically seeing - first class usually has a couple seats with an empty list, and business usually (always?) has a small number of passengers with zero seats available. I may have seen a flight or two with 1 or 2 business class seats and no passengers, but don't recall ever seeing both seats and passengers on the same list.

Follow-up question: in the cases where there are people on the upgrade list but no seats (say for a flight departing a few hours from now), how often are additional seats released for upgrades? Are all of the upgrades assigned well before the flight (and thus before the waitlists are even published), or if I appear on a waitlist with zero seats, do I still have a chance of being upgraded?