The Supercar Registry - Opinions on POP

The date on the POP is the in-service date. Which is not the same as when the car was sold.
The owner's name is supposed to be on the POP. So that's no surprise. It was put on the POP when the car was sold.
The box says 'Selling Dealer'. This is where the anomaly occurs. The GM dept put their stamp there, presumably because that's when the in-service date started.
Like I said, I've seen this several times, so it was how the system was supposed to work.

Any car that was to be sold could be tagged by a GM employee (with any leasee getting the right of first refusal). The car would then be transferred to their local dealer to for prep and paperwork. Else the cars were sold at auction. The cars were distributed to auctions over several hundred mile area so as to not saturate the local market. I know some 69's from Detroit were sold in PA.
Ford had a lot that you could peruse to see what had been turned in, but not yet sent to auction. I don't know if GM had something similar in this timeframe.