What's the evidence that they knew about those lands before 1492?
It's quite a while that I had checked these sources for my Hussite TL... I don't remember and can't find the sources which I had unearthed back then, but from what I recall, it's rather certain that Newfoundland and Labrador fishing grounds were regularly attended in the 15th century.
??? Outside of the Canaries no islands fit this, they were all uninhabited, are you saying tat medieval sailors went all the way to the Americas in a consistent fashion?
No, not to the Americas. But they went into the Arctic Sea and repeatedly encountered Uralic-speaking inhabitants on small islands along what we now call Russia's Northern coastline: Novgorodian, Norse, Swedish, and German/Dutch-speaking sailors are attested to have ventured around there, and the "Pomors" have even stayed.
To a fisher who lands at the coast of Newfoundland or Labrador, certainly these shores look a lot like Siberia's or the lands of the Sami. Cold, barren lands with fisher-gatherers, devoid of any interest unless you're after the fish or... which is in the sea, so the landmass was irrelevant except maybe as a waystation. Where would the excitement about " A NEW CONTINENT!" come from... when Siberia's Arctic was enormous and not entirely cartographed, either, and a plausible route towards China, too, if you wanted, and yet nobody gave a damn about it.
Just saying: Having stumbled upon America can't be falsified by the fact that the people who potentially did it didn't talk about it. They kept their fishing grounds secret. They saw no other relevance. If they found it, which, again, I'm sorry I can't find the texts which I had read on.