Yes, your car should have been registered as a '79. No, there is no magic to the 9th month of a year as to which year the car really is. Some manufactures put out new year models very early in a calender year, as the next year. For many manufacturers, the change-over is around the month of July. Mistakes have been made at both dealers and motor vehicle departments. I don't think it is any longer an accepted practice for a dealer to title a vehicle by the calender year in which it is sold. They used to do that, incorrectly titling left-over previous model year cars as ones from the new model year. That is now illegal in most if not all states, AFAIK.