There should be a "hidden VIN" on the car. For a 1980 I wouldn't know where to look. It is illegal (but possible) to replace the VIN tag. The hidden VIN is less likely to be replaced. If you noted the VIN on the car that you thought was your son's, try to find someone like your insurance agent to run that VIN. You could also try a carfax on the VIN for the car you spotted. If it has been totaled, then maybe someone did swap the VIN.
Good hunting, be safe
Tom