Had to look it up. If you can believe Wikipedia then the Pre B guns were made from 1980 to 1993. After that were the B and BD models, followed by other variants in a few years.
The Pre B means no firing pin block. Which means no hole through the slide for the roll pin that holds the firing pin in the slide. Does yours have that hole/roll pin in the slide? They did make, for some period, a CZ85 Combat with no firing pin block (as well as other pistols with no firing pin block) but I don't think they'd have the spur hammer or rounded trigger guard.