To add a little more info on PMUA's practice: they didn't always get BP 5A vs. 5B right.

I can think of at least two distinct instances for me. First instance was an error in my favor: I leapfrogged to the top of the list when standing by for an earlier flight on ROA-IAD, despite the fact there were about a dozen pax trying to get on it after the first flight of the day got cancelled.

Second instance went against me (karma, eh?): I got stuck in ORD during WX as a 1P. The next day, the first 6-7 flights to WAS came and went without me clearing and with many no-status pax, GMs, and 2Ps clearing. I asked why, and GA said they were BP 5A and I was BP 5B. Yet we were all disserviced pax. GA could only speculate that they had international connections in WAS and were getting higher priority than me, as I was "merely" flying home. At any rate, my cancellation was being treated as a "courtesy" standby when everyone else's seemed to be treated as disserviced pax.