Hmmm, I'm not sure about this:-
I think I'd sooner not interfere with the coin, even with the carbon spot/s there.
With regard to the point made by Sword, about the carbon spot developing post slabbing, that is entirely plausible, as they take time to appear. What will never be known is what - or who -- caused it. Quite possibly a minute drop of saliva inadvertently left on the coin's surface, because whoever was handling it, also talked at the same time. A very good reason never to talk whilst handling coins, and to turn right away if you have to cough or sneeze !!!
The tiny and unobtrusive spots on the 1918 and 1900 examples above, would not put me off to any great degree, as the coins are otherwise superb.