The stuff that happens on the line is certainly an issue, but since the customer is presumably billed for changes to the car made during the assembly sequence, the billing history should be the most accurate document.

The broadcast sheet will not always be accurate. I had a 'Cuda with a broadcast sheet full of options, VIN number matched, and there were slash marks through most of the options and red grease pencil changes "radio delete", "A/C delete", "P/S delete", "P/B delete", "covers delete" and more. There was no chance to get a billing history and I didn't get the window sticker or any other documentation, but it was clear that the car was modified while in sequence. When I got the car, it did not have any of the options that were "originally" on the broadcast sheet. It was pretty bare, with only go-fast parts left in the build.

Then there were changes made at dealer level, special packages, special options, special trim, pop in a different radio, or install wheel covers, or swap wheels from covers to Rallyes...all to make the sale.

There are also plenty of cars that wear VINs that were not originally issued to them. Swapping a dash or VIN plate is not difficult. Taking a VIN and parts from a rotten or wrecked hulk and installing it on a clean stripped chassis has been done since VINs have been around. Before PHS and broadcast sheet decoding, how would you know what the car was supposed to have? Mopars had data plates that carried far more information than the Pontiac body code tag, and you'd look to see if the engine UPC matched the VIN engine code. You can't do much with Pontiacs, just see if the VIN shows 6 cylinder or 8 cylinder, and if a handful of options are on the body code tag.