Multiple new member class?

[newsun]

How does a chapter do COB, without offering bids during certain set times? For example, I know chapters who do COB, but only offer bids during a predetermined 1 or 2 week period. All the women who accept bids during this time, become the next new member class and go through the new member program together.

I read a few posts, where it seems that the COB bids were being offered almost at any time. Do these groups have multiple new member classes? I am confused.