Brendan of the two sound like the one with the better chance of returning. as you say knowing where you are going is a big advantage. No doubt many people using the craft of the time would fail, but some might succeed.
If they did, it was of no consequence to the vaster scheme of things. Nothing effected in European history. Nothing effected in the Americas. If there were returning survivors, their stories made no impact in terms of inspiring follow-through.
As was talked about in the Rome Crossing Atlantic thread, you need a good reason to be making transatlantic voyages and you need a base infrastructure (a tech kit suited to long bluewater voyages, knowledge, incrementally arrived at of winds and currents of the Atlantic, forward logistic bases, etc.) to support it. The Norse and the Portuguese (for example) had these things. As did the Polynesians in the other side of the Planet.
But going back to the OPs original question: what consequences would occur if the Americas were discovered by people in the Old World prior to OTL? By discovery, the intent is a sustainable knowledge of the Americas existence obtained by the Old Worlders. Not one-way accidents.
It is possible to wank up the Norse contribution to this. I could see Iberians discovery the Americas a few decades earlier in the 15th C. It is even possible that a Polynesian discovery (more possible in my mind then many of the scenarios employing Atlantic cultures) via the Pacific eventually gets transmitted back across the Pacific to other cultures, probably most likely through SE Asia (Im looking at you Indonesians, Malays, Chinese, and Indians). How does this effect the course of history?
