several things to say on this:
1) yep, it's a reprint that was slabbed as an original, and the buyer made a $5000 boo-boo when it was purchased a few years ago. Here's the link from the CC forum discussion on the exact item from a MH auction, showing images of a real '69 Clemente, and the '83 reprint version, which the item slabbed as cert #81751818 clearly is:
https://forums.collectors.com/discus...mment_11686941
(like you said the most strikingly obvious difference is that the team name and the player name are oppositely top/bottom for the original and reprint, so this was a very bad mistake on PSA's part and happens b/c they apparently don't do the obviously simple thing in this digital age of using stock photos of known good items for comparison to help their authenticators along, and they don't have enough oversight to catch things like this going through)
2) I checked the cert again just now and it comes up as unknown, which is weird, b/c it's been there before (I'm pretty sure I remember checking it in the past) and b/c the pop report still lists 1/1 MINT 9. I follow this player set very closely and the odds that another has graded out in the past few days is less than remote. It's supposed to be this one, which is messed up if the cert is now not registering as anything.
3) it's come up before and why does PSA not do anything about it until now? Just b/c of all the other nonsense being brought to light? Like you wondered, what about the collector, who should be the resident expert on these. Once he figured out his mistake, why not return it to PSA and get the $5k as a refund based on their authentication guarantee, rather than try to pass it on to some other unsuspecting person, who perhaps is less likely to notice since it is now bunched in a full lot? Whether the consignment company will now do anything about it is anyone's guess. As we've all seen they've all seemed to prove themselves to be remarkably tone-deaf about the ethics and transparency that should be the bedrock of the business model. They're all just so cowardly about doing the right thing when they have visions in their head about the acute impact to the bottom line for one sale rather than the chronic effect on trust. Short-sighted.