It's a piece of the car's documentation package as delivered by the dealer. It's a warranty processing data plate with the original owner's name and address, as well as major options found on the car including trim and paint.

Having the Protect-o-plate is a plus if your car is totally correct, low mileage, or high/rare optioned. It's otherwise a novelty piece from the car's past. After 40 years it's not likely you'd be able to look up the former owner at the same address to ask about the car, but I suppose it could happen.