To be fair, GS-12 isn't that common in some agencies. Because of hiring wickets, you'll see a lot more GS-11 or 13.
I don't know any GS-12s that don't have a Masters. Most would have come in as an 11 with a Masters, then promoted to 12. Extra skills would have earned additional extra steps (steps are 12 different levels of compensation between grades). Of course it's possible, but in my agency unlikely.
Also a GS-13 would be equivalent to a half bird Colonel. 14/15 would be full bird. SES levels would be equivalent to the different general levels.
https://www.opm.gov/policy-data-oversight/pay-leave/salaries...
A mid-grade GS-12 in SF/DC/NY makes 100k+ which would be a non supervisory Individual Contributor with a BS.
Colonel equivalent (GS-15) is indeed rare and would be closer to $150k+