is this right?

If every house cut someone, then they could still be dropped from recruitment, but if no one withdrew, then yes, quota could have been around 90. If you make it to pref, attend all the pref parties you are invited to and list every chapter you attended pref for on your MRABA, you are guaranteed a bid to one of those chapters. If you are not placed through regular matching (you're too low on the lists of all your chapters), you are placed at one of your options as a quota addition because you played by the rules. The issue of quota has nothing to do with there only being a certain number of spots. Quota is simply the number of women signing MRABAs divided by the number of houses and then you have about a 5% window so quota could be slightly less than exactly what that math problem would result in. When determining quota, they also look at how many houses make quota at a certain number, the total number of women placed and the percentage of women that get their first and second choices.

The way it works at most campuses is that about 80% of the girls who start recruitment will make it to preference round. Of the 20% who don't, some are released by all sororities and some choose to drop out. Quota is determined by the number of those attending preference (could be to 1, 2, or 3) divided by number of sororities. So, if OSU really had 1300, if 80% of those had made it to preference, that is a quota of 74 per sorority. The more people who drop out, the lower the quota is going to be. At many campuses, girls are promised a bid if they attend preference and list all their options.