On this topic (parallel postulate), it took ~2000 years from Euclid and then 3 people all came to the same conclusion independently within ~10-20 years.

Progress is weird.

Is it so weird? See Multiple discovery https://en.wikipedia.org/wiki/Multiple_discovery and Zeitgeist https://en.wikipedia.org/wiki/Zeitgeist namely that there might, or might not, be objective knowledge out there describing properly an objective World but we as a specie do chip at it with itself over time. When a new discovery in any field is made it propagates through our social network and tools we have for it, e.g. cafes, scientific journal, Web. As soon as something is discovered most of us connected enough get the new tool or perspective, update our Worldview and chip it at it again. IMHO this way it seems pretty normal that things hitherto unknown, no matter for how long, become knowable to seemingly independent discovers.