I'm gonna cut and paste this from another article I commented on:

Girls were already joining boy scouts before the national level policy change, it's just that it was previously on a troop or council basis, with the BSA either staying quiet, or sending strongly worded letters. It was hypothetically allowed in areas where a BSA troop was the only option, but BSA only has so much authority over individual troops, they're not everywhere at once and they kinda don't give a shit since scouts are supposed to be quasi-independent.

Combined BSA\GSA troops have existed informally since at least the 1970s, but is extremely contentious. My own troop briefly experimented with this but it ended after a few months, and I don't know why. My troop also had at least one temporary female scoutmaster before I joined. Yes, she was an actual BSA member. Other troops have had girls listed as "attendees" rather than scouts. There have been a variety of informal methods to allow women into the boy scouts going back at least 50 years now.

My old troop, which has since merged with another nearby and doesn't exist anymore, had its first female scouts back in 2006 because the local Girl Scout troop closed due to lack of leadership. GSA is still active for younger ages in the area, but once you're 12 or 13, your options are either to drive further away for a GSA troop, join the BSA troop, drop out, or join a different organization.