Webb, as George mentioned, it was originally on an index card that went down the line with the vehicle. It was transferred to either micro film or micro fiche for permanent record keeping.
Todays cars have computerized records, but there is still a paper copy of the "Build Sheet" that accompanies it down the line. And, you'll find a list of the options the car is equipped with somewhere on the vehicle. Inside the glovebox, for instance.
Jeff