Just so all of us have a better understanding.
A vehicle identification number (VIN) is a unique code, including a serial number, used by the automotive industry to identify individual motor vehicles, towed vehicles, motorcycles, scooters and mopeds, as defined in ISO 3779 (content and structure) and ISO 4030 (location and attachment).
VINs were first used in 1954 in the United States.[1] From 1954 to 1981, there was no accepted standard for these numbers, so different manufacturers used different formats.
In 1981, the National Highway Traffic Safety Administration of the United States standardized the format.[1] It required all on-road vehicles sold to contain a 17-character VIN, which does not include the letters O (o), I (i), and Q (q) (to avoid confusion with numerals 0, 1, and 9).
Many VIN verification services are looking for the 17 character number so may give a "VIN unrecognized". That does not necessarily mean that the vehicle serial number (precedes the VIN) is bogus.
I don't have my serial number book handy but most automotive manuals (Motors, Chiltons) and similar have a listing of Serial number sequences by manufacturer.