Global trade was a thing back then. It collapsed around 1200 BC, but before it did, there was a lot of knowledge (and probably cultural phenomena) spreading around amongst much of humanity.
No, that's likely to end up in the half we'll never be able to figure out. Unless the aliens are good at record-keeping and decide to tell us one day. :D
Assume the OP's point is that American civilisations developed without being plugged into a Eurasian 'global' trade system, starting in Peru. The Norte Chico system is generally believed to have developed cities and monumental architecture over a broadly similar time period as the Middle Eastern civilisations without any contact with them at all. They even built superficially similar step pyramids.
I doubt we'll ever know half of it.