which houses typically COB

Spring 2026 COB chapters

Alpha Xi Delta
Gamma Phi Beta
Kappa alpha theta
Kappa kappa gamma
Sigma kappa
Sigma sigma sigma
Zeta Tau Alpha

You should not be expecting a COB this fall because most chapters don't typically COB after bid day, and if they do they bid girls they already know who didn't get a bid because they either dropped out of recruitment or SIP'd. A pnm isn't going to get an open bid from a chapter that dropped her before pref, or maybe before sisterhood as a stretch, or any pnm they don't already know.
The best chance for a pnm to get a bid is during formal recruitment because the process is geared to maximize the number of pnm's receiving bids, not to remove pnm's from the process. There is not a set number of bids to give out, quota isn't set until after pref when all the pnm's have signed their cards and is based on that number. Any pnm who makes it to the pref round is guaranteed a bid if they rank both their pref houses, or just the one if that's all they get back.

COB in fall is not a major thing and would only happen for chapters that don't bid to quota, which all of them basically do, or for chapters that are still below Total after it is reset by panhellenic on bid day. So it depends what the new Total will be and which, if any, chapters fall below it to be eligible. There are never many Open Bids in fall because as stated quota is hit and total is reset to reflect the new membership numbers. There aren't that many in spring either, it just depends on how many members graduate in December or otherwise decide to drop out and IF that puts a chapter below total and IF they decide to fill an open spot.

COB is not a secondary recruitment or a backdoor to a bid, it is nothing to rely on if you want to join a sorority.