Hope this never happens again, but

[Dennis Nicely]

In my humble opinion, one official has to concede to the call of the other one. In situtations like this, I make it a point to walk away from a conference with my partner(s) with one or the other call standing. Coaches, fans and all other observers have learned to accept officials' judgments. They are less inclined to forgive competing egoes.

Based on your description of the situation, my instincts tell me the PC foul would stand. A1's outstretched arm would probably come into contact with some part of B1 prior to B1's body coming into contact with A1. But of course, I wasn't there and neither was my ego.