Nothing's Forgotten, it's all written down somewhere and odds are good that any random peasant has, I don't know, ten volumes of Elminster's "I Was There Too, And Weird Things Happened To Me While I Made History; With Appendix On Legendary And Unique Creatures Likely To Be Encountered In The Area And How I Beat Them" in the root cellar.
I played the NeverWinter Nights demo, and just browsing bookshelves found out a bajillion and one obscure historical details. I don't think anything about the Realms is forgotten, except perhaps the Forgotten part.