Maybe someday, we can only continue to press the issue with eBay. At least they kill auctions containing VINs and that's a start.
Evan Alan Colvin's books say he refuses to publish specific information on accessory codes on trim tags. Some GM tags have specific (and desireable) codes but many do not; some GM lines and plants do have accessory codes such as some (but not all plants) of the 64-67 Chevelle tags. Most of the time these codes are harmless enough and there are some that appear to be plant specific. Reproduction tags do come into play here from time to time such as a 66 L78 convertible initially being sold a couple of years ago. Problem was these codes showed a Powerglide transmission on the trim tag.
Later the same car shows up with the trim tag showing a 4-speed. Same body date, job number, body number, interior and paint - but now group 2 shows "L" instead of "M" code.
While accessory codes can help build a bogus car, it can also find bogus cars like this 66 L78. Many other pieces of information such as engine/transmission casting numbers and dates are readily published to aid the building of a bogus car.
BTW, anyone with <u>known</u> data on some 64-67 group option codes for Chevelles, I would like to hear from you.