Is there really a method to the madness? (Upgrade priority) - mystery solved!
I have long suspected that the timing of upgrade request does not always control (even within the same tier, same connection status, and same fare basis), and now I'm sure of it.
My S.O. and I were required to attend the same conference in D.C. this week. I booked and ticketed my flight the night before she did (totally separate itins -- not linked). We are both EXP, had the exact same itinerary (LAX-ORD-DCA, and the same route on the way back), the same fare codes (L on the outbound, S inbound), and paid the very same price.
We both were upgraded on the ORD-DCA segment at around the 100 hour mark, but while I got the upgrade on the (763) LAX-ORD segment, she ultimately went to the airport list (where she was 2nd, and got the upgrade).
Last night, at the 100-hour mark for the return, she got her upgrade for the DCA-ORD segment, and I didn't.
I can't think of any explanation for the inconsistency other than that when all else is equal, upgrades at the 100, 72, and 24 hour marks are distributed at random rather than by upgrade request.