I mean, it's an interesting discussion, and I probably came a little hot there, but the thing to realize is that the only reason for all the eastward voyages was no one knew yet exactly how far to the west you would have to go. People did sail west, and had been doing so for quite some time since the Vikings and maybe earlier. The thing Columbus did was sail west specifically to get to the East Indies. Which of course he totally fucked up. Remember everyone knew this pretty quickly after he hit the Caribbean, Magellan went all the way around just a few decades later. And it was all because Spain was racing Portugal to get there faster. Columbus or not they were sending people there as quickly as that could, there absolutely no way America lies undetected for another century if Columbus doesn't show up.
The question isn't really about Pre-Columbian expeditions, but Pre-Columbian contact where it becomes a big question if anyone came before him from Europe. Remember we are talking about this in context of hitting North America, not whether anyone was trying for the East Indies.