Especially anyone that does the steel shoots or first Wednesday lunches. Have a few mags I think are pre B but no longer have one to test them on.
The B is newer version of the original CZ75 and has 75B as model that stands for firing pin block that the originals didn't have. The mags are slightly different dimensions. 75B can use either but the pre B can't use 75B mags. Unfortunately close enough that measuring isn't good enough.