Is it that there is no mint mark on that coin making it from the Philadelphia mint but the company said it is Denver? But I can't really make your photo large enough to be sure there's no mint mark. I'm just guessing.
Yes! You are correct! @LaCointessa The 1944 Nickel had the Mint Mark on the Reverse side. This is actually a P Mint Mark. So NGC made the mistake calling it a D Mint Mark, so it's considered an Error Label
NGC would consider this a "Mechanical Error" and will correct the slab for you. Every time I've had one happen (got super excited because I had one coin show up in the Completed Invoices as a 4-figure coin...only to find out it was a D and they'd slabbed it as a P. A P worth substantially less in the same grade) NGC has always covered shipping costs both ways (plus the grading fee.) Of course, that's a coin I personally submitted. Not sure how they'd react for one found in the wild.
I would probably keep it, cool error that shows that the big grading companies aren't always perfect. Beautiful coin, I like the toning.
