I have seen a history in Hemmings Muscle Machines of BJ cars being sold at other auctions within 12 months or so and the cars typically loose money.
Yes, they lose money compared to what they were sold for at the BJ auction. But they gained on 'like cars' that didn't have the BJ auction history documentation. I've seen accounts where cars get a 10% 'bump' just because they are documented BJ cars. Ironically, that's what was paid to push them through by the seller and buyer. So it's a 'wash' in the short run. But it's a plus when buying a car that has went over the BJ block. This could all be a fad and a very short term gain.