I'd like to add to this.
I have invoices "Tentative" price (Invoiced 5 days before build) and "Firm" price (one month after Sch Build Date) along with an order form that I obtained from the owner of a dealership (dated end of june '67) in 1987 or 88 for a car I had recently purchased..
The vehicle purchase order form has the order number written on the upper right hand corner AND the VIN is hand written on the form in a field labeled Serial Number. The invoice has the same order number preceded by the following 927-GW-109### <-Order Number. Car is a St Louis Coronet scheduled 927 (on fender tag). The order number is very low 109###. I'm assuming orders started with 10##### every year. I'm guessing that Invoice number is the scheduled build date, St Louis Coronet and the order number.
There is also a "List No." that differs between the two invoices thus 4090-01-3016 on the Tentative and 4090-01-3501 on the Firm. Both the invoices have the complete VIN.
Other interesting items are the shipping route. It's designated G43 SLSF-QA&P-ATSF-SP-OAKLAND-CCI (St. Louis–San Francisco Railway, Quanah, Acme and Pacific Railway, Atchison, Topeka and Santa Fe Railway - Southern Pacific Transportation (Rail), Oakland (Rail terminal?), and finally CCI a Truck Transport Company. Also included is money info (record of a CD (Certificate of Deposit) at a bank local to the dealership.
I've not seen these documents any other time and obtained. FWIW it appears the dealer made only about $200 and any profit on the trade-in on the sale.