I recall reading an article a few years back stating that NGC had identified five 2014 Great Smoky Mountains Five-Ounce Specimen coins with a significant mint error: they are missing the “P” mintmark. My understanding is that for such an error to occur, a die would be used that was missing the “P” so I would think there would be at least a few hundred such coins, assuming that many would be struck with each die. Or, mint personnel noticed the omission and removed all but a few from distribution. I would appreciate your thoughts or any updated information that you may have come across. Thanks.
A coin missing the MM or any other letter/device is from what is called a grease filled die. The area missing was debris filled. When the letter is filled completely it acts like a smooth surface. So far 5 of these have been found, but could be more depending on how long it took for the debris grease filled element to become dislodged from the die face.
The P mintmark was more than likely covered in grease and or other debris. It sounds like only a few were struck before the debris was removed or fell off of the Die. It's possible there could be more but good luck in finding one.
I looked it up. It was NGC. 4 were in a submission from modern coin mart and a 5th came in separately. The grader noticed it according to them. "There are two versions of these five-ounce issues: a Mint State version, with a reflective finish and no mintmark, and a Specimen version with a “vapor-blasted” matte finish and a “P” mintmark. The Mint State versions are sold through US Mint Authorized Purchasers, while the Specimen versions are sold directly to consumers by the US Mint." And there you have it I suppose. Likely it's a filled die error and not missing from the die as was already said although the image of it looks like it was never there in the first place suggesting they grabbed the wrong obverse die for a MS version, "vapor blasted" it and struck something until it was noticed or it went unnoticed... there doesn't seem to be any disruption in the finish where the P should be on the example shown on NGC news on their website and I'd expect the mate finish to have been disrupted by a filled die. This story went way under the radar I suppose there's maybe more out there that people bought, and never noticed it yet.