Do you have the manufacturer's ID plate on the driver's side door post? This would be the only place on the AD trucks that an ID number would be found. As Wally pointed out, the "VIN" number you have may have been taken from the engine. Some jurisdictions assigned a state created VIN number.
If you do have th ID plate, you can definitely identify the year. If not, you have to use some of the other characteristics of the truck to help identify the year.
