I think there's also a point everyone who talks about other "discoveries" of America purposely ignores. This is about the discovery of it not for Europe the continent. This is about its discovery for what was the civilized nations in Europe. So if we look at Iceland - a place that's essentially a standalone island already half way to America - where a bunch of vikings lived who at the time weren't hanging out with people from places like Spain or Italy or France - it's an apples to oranges comparison.
First Iceland is only half way to North America if you consider Greenland (which is kind of weird since both Iceland and Greenland are islands between the two continents). The distance between Iceland and Labrador is twice as long as the distance between Iceland and Norway. And the double distance is on top of much much rougher seas of the Labrador sea then the North Atlantic. So for small sailboats Europe is definitely close while North America isn’t.
Second, people traveled a lot both to Iceland and from Iceland in the centuries after the voyages mentioned in Grænlendinga Saga. Ships went to Iceland to trait, or fish and people went from Iceland to continental Europe for pilgrimage, trade, etc. These people definitely talked to each other and told each other stories of their ancestors. I wouldn’t be surprised if some Portuguese fishermen were told Grænlendinga Saga while wintering in Iceland sometime in the 14th century after their trip home was delayed for some reason. Or that a pilgrim from Iceland told a fellow Spanish Christion in broken latin about Leifur Eiríksson on their way to Rome.
Third. Flateyarbók (which contains written stories about the norse settlements in North America) was written down in the mid 13th century. The Icelandic sagas were coveted by Scandinavian royalty and I bet royalty in both Norway and Denmark knew about it’s existence, and might even have heard Grænlendinga Saga recited.
Now it probably wasn’t common knowledge that there were lands west of the Atlantic which people once tried to settle, but it probably wasn’t unknown either.
It is not hard to imagine an alternative scenario where by some freak luck Christopher Columbus happens to talk to a person who’s great grandfather told a story about an Icelander they walked part of the way to Rome with. “Curious folks those Icelanders”, they say, “in the old times they used to sail all around the world. Even going West of Greenland”.
“Greenland? You mean the icy land way north in the Atlantic where they get those Walrus husks?” Columbus replies.
“Yes, there! Apparently there are some much more favorable lands south west of there. I wonder how much further south it reaches, maybe as far south as Africa?”
Or maybe a scenario where a common crewman on Columbus’ voyage knew about these stories from a Basque fisherman who in turn heard them while on a fishing trip to Iceland. “This isn’t Japan”, he claims. “An old friend of mine heard stories about lands as far west as this—albeit further north as well. Maybe these islands are of the same island chain which lie between Europe and Asia”. This crewman is promptly laughed at. “Off course this is Japan, our captain says so.” They say, and the crewman never mentions it again.
