If I remember correctly, somebody bought a run of proofs from one of those tv guys, submitted a bunch of coins and got back the PR-70. They sold it and the buyer was none to happy. I'm shocked that NGC didn't call it a mechanical error and walk away. To their credit they stood by a very costly mistake.
This was years ago so I cant provide a link. I think coin was purchased for 40k and developed a spot. Can anyone else elaborate ?
Actually the 1963 Lincoln was settled for 40k by PCGS rather than NGC but it was years ago and I'm sure the link is easy to find if you know where to look.