how does cob work

COB is a more relaxed style of recruitment. Some PNMs shine better in COB than they would during formal recruitment. A chapter which is doing COB will invite a PNM to a series of events during which they can meet some of the sisters. If the chapter likes you, you will be issued a bid. Generally there is a limited timeframe in which to accept or decline the bid.

The more popular chapters likely already have women in whom they have an interest. So even if they are doing COB, you may never hear about it.

I would say, pursue any opportunities that come your way. If you like what you see, accept the bid.