I think @paddyman98 already gave an opinion on this coin and that he believes it is a foreign substance (crud). This is the same photograph you posted the other day. If you want a second opinion, at least please provide better photographs of this coin including a close up of the area of interest which contains what you are calling "falling mint mark." Good luck on your second opinion!
You probably need to send it in to one of the major Third Party Graders in order to legitimize it. If one of them says its real, you're in the Big Bucks. Without one of them saying it's for real, it doesn't mean a thing. Do yourself a favor, take a wet wooden toothpick and see if that dark stuff comes off. If it's just crud, it will come off. If it doesn't, it may be real. Either way, THAT is your first reality check !
@Doug swanson There is a Mint Error known as a Dropped Element or Isolated Element but when you read what it is you will understand how it occurs. Mint Marks just don't fall off and end up on another part of the coin. http://www.error-ref.com/struck-through_dropped_filling/
You should. And make sure you get back to us with the results. https://www.ngccoin.com/submit-coins/how-to-submit.aspx Try NGC. I have been with them for many years.
Great. And if it comes back good I will share with you some of my hundreds of Mint Errors that I own.. I specialize in Mint Errors
That is a foreign substance on the coin, not a dropped element. Hey @paddyman98 have you ever been stumped on here? Told someone that they had a damaged coin, they sent it in and it came back as an error? I don't think I have ever seen it with any member here. I may be ranting but if someone doesn't like the advice they are given why did they come here to ask the question anyways?
At first, I took the T-Shirt at face value but then I got suspicious so I zoomed in. Hahahahahahahahahaha!!!!! You hog the bed with your coin collection and she hogs the nightstand and closet with her cosmetics and shoes and bags - so that's what makes a marriage work!