Association of the term Produced with the VIN.
The VIN is administrative. It is not related to the number of cars produced nor the order of production. A VIN is simply a number assigned to a specific car. (We can count the number of apples in a basket but that does not tell us in what order they were picked.)
1) Research leads to the possibility that blocks of numbers were not simply not even assigned meaning if we don't use a block of, say, 500 VINs that alters the associated VIN assignment compared to production. A car is likely not the XXXth produced at the plant. It may not even be the XXXth VIN assigned.
2) There are instances where US sold and Canada sold cars use a different VIN range. There are instances where car lines start in the 500xxx VIN range. There are instances where out of sequence VINS are assigned (a block of 400xxx VINS for '69 Lynch Road). Associating production with a VIN would drastically overinflate the number of cars made for a certain plant for certain years.
A VIN does not matter to production. As we do more research (see the documentation being accumulated in the "The Last C body Produced" thread) we find more and more supporting evidence this is true.
What you are doing is important. Please keep at it. This is an opportunity to be accurate where others have not.