Each plant had the same sequence of VINs. They ALL started the model year with 100001, but since the assembly plant was also in the VIN there could not have been any complete duplicates. Usually the first few were pre-production, press cars, etc. Production started around Aug 1. Certain cars were only produced at one plant while others could have come from a few places. ALL '67-69 A-body convertibles were built at Dodge Main, AKA Hamtramk.
Also, the cars did not necessarily come off the line in numerical order as the VINs were produced before the car started down the line.
