There was really really good thread explaining it that I can't find right now. But basically, even I could understand release figures after reading it.
ETA: Found it!
This is the one I was thinking of, it was stickied in Recruitment Stories and not Sorority Recruitment which is why it took me so long to find it:
NPC Quota, Release Figures and Quota Additions
This one will also have some relevant information:
After Several Years: What Do You Think of the New Release Figures?