Here's an in-service label very close to your date:
One interesting thing I see on your assignment card is that your car was one of the runouts that was sold at Downtown Ford (Senator Ford was used too-both were located in Sacto.) and not at the Motor Transport lot. For a period, many retired Mustangs were sold off this way. I think it was an experiment to see if paying a commission to the dealers, and possibly having them perform a higher than normal amount and quality of refurbishment, would be a more lucrative and/or efficient means of moving these units than sending them to low-bid body shops for cheap resprays and then selling them at the M/T lot. I have heard stories about how nice some of the Mustangs sold at the dealer lots looked but I guess in the end it may not have panned out for the parties involved because the practice has not endured beyond the Mustang era. If anyone else has any knowledge about this arrangement I'd sure like to hear about it.
Also, judging from the plate numbers listed it looks like your car probably replaced an '80 St. Regis sedan and was in turn replaced by an '84 Mustang.