early start

A good majority girls who are already followed by actives are friends with one another/from the same hometown. And no, a lot of "rushing" hasn't happened... A follow on insta does not equate to a bid, and honestly doesn't even mean the sorority is that interested in you, they may just want to check you out and see what you're like. A lot of actives are trying to follow PNMs right now because in a month all of the following and commenting will be considered dirty rushing, and the sorority thus gets fined for that. And yes there are some houses that have "lists." But it's not as formal and concrete as it sounds... Some sororities, usually old row sororities that place a heavy importance on connections, have drafted lists of girls they're really going to recruit hard. But obviously that's not set in stone, a girl who's on their radar can come through rush and completely disappoint them while another girl who signed up for rush the week before can come through and blow them away.
As of right now, you're not too late to anything. I'd suggest to add yourself into the rush Facebook groups and groupmes and also get started on finding people to write recs for you if you want to have a more competitive edge during rush.

The response above is perfect. Bump so the late deciders can realize they may be just a tad bit behind the "known" and connected pnms but they have plenary of opportunity.

Relax - you're not behind. It all means nothing.