if you are talking about the area in between the N and M. That is just a period. NORTH MARIANA ISLANDS = N. MARIANA ISLANDS. I don't see anything else that looks like a missing letter.
I don't see any missing letters, but it looks like it was struck with a very worn die which is making everything look mushy. You can also see the radial flow lines from the die wear. Interesting, but no added value
