So invisible colleges are a real thing, referring to basically independent circles of scholars who share materials. Is the concept of heroic invisible colleges who fight monsters and wicked sorcerers and try to cultivate knowledge for humanity a pre-existing thing in occultism or is that an invention of this game?
It's based on the first, original Invisible College. This was an independent non-centralized movement of writers (mostly in Britain) who were re-examining the works of the Rosicrucians a generation earlier, and trying to advocate for a more free society, "tolerance" (free speech, not the modern version of the word), religious universalism, and the promotion of knowledge and learning. The writers of the original Invisible College were among the founding members of the Royal Society, and the first Speculative (ie. Modern) Freemasons.
Anyone who uses the term "invisible college" today, got it from those original guys, including luminaries like Robert Moray and Elias Ashmole.