As Cricket67 notes, you should find a date on the gun in one of the little insets on the slide just to the rear of the ejection port. My 85 Combat is dated 99, while my pre-B CZ-75 is dated 85
It may be low mileage. The lack of color on the slide railes may or may not indicate high use. Someone may have taken time to sand/file/polish the rails. (My '85 CZ-75 shoots as accurately as my 85 Combat, and has a better single-action trigger, to boot.)
As long as the gun is kept up, with a good recoil spring, and the barrel not shot out, it really shouldn't matter all that much how much its been shot.
Generally speaking, if its high mileage and still looks good, the prior owners probably took good care of it, and you need not worry.