Medicare.gov says, "The cost of Medigap policies can vary widely. There can be big differences in the premiums that different insurance companies charge for exactly the same coverage."
That is, all supplemental plans with the same letter are identical and there are no insurance carrier specific differences.
Stupidly complicated. You can pay more or less for exactly the same thing. Kind of like West Marine vs your local low cost chandler.
Craig, SN68 Sangaris, Tropic Isle Harbor, FL