I feel like the term "discoverers" discounts the existing human residents of the Americas who also had written histories: e.g. the Mayans, whose written histories were largely destroyed by Europeans. I get what you mean though: how else are we to know now about what happened then without written records? It is just sad how much has been destroyed.

The potential of lost written history is fascinating to me. The Phoenicians of Carthage had boats which were capable of crossing the Atlantic and were known to take journeys well past the straights of Gibraltar, but a lot of their written history has been lost thanks to the Punic wars of Ancient Rome. It would be a fascinating lost episode of history if the Phoenicians "discovered" the Americas well before Vikings or other Europeans did. For all we know, this could have happened but accounts were simply lost to time.