Whatever one makes of the Stone itself, it is now generally conceded by neutral observers that Scandinavians had been visting parts of North America for centuries, even millennia, and there was probably an ongoing knowledge of sea routes, currents, etc. handed down among mariners there.
What we NOW need to get admitted and established, is that "Vinland" was not just a name, but an established colony that, like Greenland, lasted some 500 years and had, in its heyday, thousands of inhabitants. Note the comment by Roger Williams that in his view, the inhabitants ("Indians") of Narragansett Bay were "for the most part descended from the Icelanders."
Above all, note that -sett on the end of the name of the bay. Only in SE Mass and Rhode Island, of the whole Atlantic coast, do we get all these place names ending is -sett, which is pure Norse as in our words sett-ler, sett-lement, etc. It means a place SUITABLE FOR HUMAN DWELLING, a place ACTUALLY INHABITED BY civilized=Norse, people. A sett-lement, IOW!
Look at the map of Mass & RE, look at the number of place names. Narra-gan-sett is the real biggie, that bay was their favorite spot, site of the Norse Church whose Newport Tower is still standing. Narra="foolish"; gan="voyage"; sett="settlement, homestead." Apparently someone set out on a voyage considered foolish or dangerous, and discovered this marvelous bay. A large runestone at the entrance to N.B. warns that there is danger from wolves and bears but come on in anyway. Indians are not mentioned.
Anthracite coal from Rhode Island was discovered at the Norse sites in Greenland, btw.