I think there were three main variations (before the dozen other modern variations)

The first series (1975 to 79)

The rail were shorter and the scalloping was further behind

Made in Czechoslovakia on a single line. I think those were blued



A good video about it

First Model CZ 75 - YouTube

The second series (pre B) had longer rails, the scalloping was more in front and Made in Czechoslovakia on two lines. Those were painted black, and the finish can be quite fragile and fall off in flakes when worn.



Then the 75B with a different trigger guard, round / combat hammer

Made in Czech Republic