I am not sure what PA and PB are--my ignorance. However, every time I speak with the 1K desk on upgrades and the agent actually is responsive, (s)he says something like: Your chances are excellent because you are the only 1k on the list or There are already a lot of 1ks on the list but I can't tell you where you rank. At the RCC, I have been told, "You are on the upgrade list, but there are 1Ks who have already flown more miles this year than you have."

The message I get is that: (1) status matters most; (2) price paid ranks second; and (3) miles accrued is the tie breaker. Time on the wait list is irrelevant. On a recent flight, my ticket was purchased close to the last minute (government) and it looked as if I was in coach. But I got to the airport and was told that I was number 1 on the waitlist (with 2 C seats available!)--and it cleared at the gate. I know from sources at UA that the list was rather long.