the usa rivet was made up to 1980 in steel, and in gold both types were made for a longer period, maybe 10 years longer.
So a mid 1980's Date could be a older model from 1980, on a usa rivet, sold a few years later. It sometimes happens.
Best is to check the serialnumber to see if it is 1980 or thereabouts. If it however is a 8 mln number for example, I doubt if it is original to the watch.