It looks like PSA really messed up the wiffle disks in the begining and have been correcting their registry. I found a "1976 STEVE GARVEY" with an older PSA label. Probably at the time they thought it was 1976, but if you check the certification number on PSA it is listed as a 1979. The new owner can submit it for reholdering and re-labeling for a fee (as a PSA misrake, I think they would fix it for free to the original submitter, but since its for sale, the new owner would have to pay to get it corrected).
I'm not a hoarder, it's a "collection"....
Joseph