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Technically there IS an upgrade list at T-96 - and before and after. There's a upgrade list at anytime anyone asks for an upgrade (or due one, like GSs at T-120) and one is not available. Up until check-in time (not necessarily T-24 for those connecting from earlier flight(s)), the tool-accessible flight status actually shows those who have upgraded via miles+$ or / instruments. Maybe you're thinking of the visible waitlist, which doesn't begin populating until people start checking in. Then there's the waitlist we can't see, which you can't see...