cob in the spring

Yes.

So basically COB happens if sororities need members to meet chapter total, so it varies year to year who does COB. I know when I COBed it was the first time my chapter had in 3 years and in the time since (3 years) they haven't had to.
I was also invited to two different chapters COB events.
I got those invitations because I really put myself out there my first semester of college and made friends with as many people as possible and talked to them about my interest in joining a sorority. So yes, it's very much about who you know! If people like you they will pull for you to become a member if there is a chance through COB!
If you really want to COB focus on pulling your grades up, joining a club or organization, becoming friends with girls in all the different sororities, and truly if it's meant to be it'll happen!
Good luck!!