Dave I split your post from the other to make it easier to find.
Yes, your tag shouldn't have D80, so the tag is a reproduction. As for the car being a real Z28, you'll need to look for other clues. Unfortunately, with a repop trim tag, everything on the car is now suspect, but there's still hope. What's the VIN? We may have it in the database. Also post a picture of the trim tag if you can and the engine pad. If the engine stamping is correct, you'll still have a Z28, but with a reproduction trim tag.
And welcome to the forum by the way.