OK, here's a slight variant on priority, if anyone can educate me. Say a pax has a route like SFO-HNL and requests upgrade with miles or CR-1 at the time of booking (and the pax status is lower than 1K). United only waitlists the pax. Then, another pax comes along inside the 100 hr window, books and tickets the flight, also waitlisted, but using 500 milers for his upgrade.

Also, for argument, both pay a similar fare and are in the same fare bucket.

So, when UA opens the upgrade inventory shortly before the departure, does the 1K guy trump the other pax who has lower status (but such lower status pax had tried to upgrade with a more potent instrument---say CR1, or even SWU or miles)? If anyone knows, I'd appreciate it.