1260 pnms too many

There is nothing limiting the class size to 70 if people stay in recruitment and maximize their options, as quota is not determined until pref round. Quota goes down when people drop out, as it is not common for people to be released completely. The more people who stick to it until the end, the larger quota will be and thus larger class sizes.

This is actually true, i know for a fact many sororities have a number they shoot for. Often after each round theres a number too, like the top usually take around 600 into the second round, which is why their lines look shorter. Each sorority it different, but the one I know the rules for wants about 75 girls

That's not how it happens. The sororities have no say in the numbers they can invite back. They are given those numbers by panhellenic after each round. The number of invitations for each house allowed each round is not predetermined; it is based on the numbers of pnm's still participating, the return numbers trending for each house, and the past few years of return rates for their house. Quota is only determined after all pnm's have signed their cards after pref. Quota is the same for every house and is larger or smaller depending on the number of pnm's, not a preset limit. Sororities cannot 'shoot for' a certain class size; it is not their choice.