Certainly, a copy of the original production order will nail down the exact date the truck was built. But there are other ways to determine the model year. Stude published starting/ending serial numbers for each model year in several ways. The truck data books contain lists of such numbers for the previous ten years or so. And the company provided a list of starting serial numbers to all state/provincial DMVs and all of its dealers in dealer service letters each year. Frank D, Dwain G, and I have provided copies/scans of these to a number of people in the past, and all have been good enough to convince a DMV of a truck's model year.