The Vikings are known to have built a settlement, it’s in Canada, an objective fact. Their explorations of this continent was preserved in their literature, again, an objective fact. The Vatican even recorded a Bishop of Vinland. It would be surprising if there were not more to be found, time will tell.
Beyond that, there is plenty of evidence that plenty of other people made it. There’s a Roman-era wreck loaded with amphorae near the coast of Brazil. Naturally, the various claims on these land are solid, but some people believe any prior visit somehow undermines their claims, so the wreck is unexcavated and the matter is closed in Brazil.
If I find the best fishing hole in America and tell no one, is it considered discovered?