The other problem, I see is;
1. VIN's that have been installed on another vehicle to make it street legal.
2. VIN changes due to "quiet" titles, salvage titles, etc.
These and possibly more, would realy skew the results.
It really wasn't until the 17 digit/character VIN came out that a lot of the vehicle and it's options could be tracked. In fact, there are still some issues with such Optional items such as ABS and the like. The VIN will tell you if it was optional, but not if it is installed. OR if was installed aftermarket.
I'm currently working on a VIN verification/Year,Make,Model project for a client and even then, it's still hard to tell on the newer vehicles what is on the vehicle and what is not.