Sorry about the little cryptic post earlier.
The original CZ75s had short dust cover frame and no firing pin block.
When they added the firing pin block system, they rebranded the guns as CZ75B.
It is an additional mechanism that lifts a lever as the trigger is pulled. This lever unblocks the mechanism that prevents the firing pin from moving. It is like the Colt Series 80 1911 where the firing pin remains locked unless you actually pull the trigger. This mechanism adds some weight to the trigger pull and makes for a longer reset. This system is also present in CZ85B, SP01, CZ97B, CZ75SA and their Decockers.
CZ still produces some guns without this extra mechanism for the competition markets and they are CZ85 Combat, CZSP-01 Shadow and CZ75 Shadow.
The removal of the extra mechanism from a CZ75B or std SP01 to address the trigger issues used to be a popular modification for a "poor man's Shadow" until NROI ruled against it for USPSA Production. (If it came from the factory without the extra parts or holes for them in the slide, it is allowed in Production Division. If it came with the parts, they can be polished but they need to stay in the gun)