The '80 and '81 fender is flat from front to back on the sides that bolt to the fork. The '82 and '83 fender is wider, and has a narrower recessed area where the fork mounts to the fender.
Make your own conclusions with that in mind. Look at ebay auctions and you'll see the difference. But don't go by what the sellers say, go by the pictures of the fenders. Most of the time the sellers don't have a clue what fits what.