I believe the Green Book suggests the max allowed quota additons to be 5% of quota. So if quota is 55, a chapter could take a max of 3 more as quota additions. I don't think total factors in to who's eligible to take additions.
I think Barbara can clarify but I think QA works similar regular bid matching to try and match girls with their first choice. But if her first choice maxed their QA before she comes up on their list then her second choice would get a shot at her.
Now that we've had a more thorough explanation of QA I have mixed feelings about the process. In the old school days if a girl failed to match to any of her top choices she either didn't go greek or
started to consider other chapters in COB or as a snap bid. Chapters that were smaller (and may have had added stigma just because they were smaller) had a better shot at these girls and turning their numbers around. Now NPC leans more towards favoring the PNM instead of the chapters. I guess they'd rather have fewer chapters that are bigger than more chapters that are smaller. The way I see it is that if a smaller chapter is struggling, QAs takes a sizable chunk of their PNMs out the equation.
Which really stinks because we've all heard stories or have sisters that end up in houses that they would never want to be in only to find they'd never want to be any where else!