Here's the thing about Shar's storyline. With both FR novels and FR TT modules, WotC often had a common phrase they used for the *big* storylines: an RSE (Realms Shaking Event). The Twilight War, as depicted in the FR novels trilogy by the same name, was labeled by WotC as an RSE. An RSE is definitely something people all across the Realms would know about because it has very widespread effects on people and places.
In this particular RSE, the entire country of Sembia was destroyed in a war in which Shar worked with the Shadovar archwizards of the returned ancient Netherese flying city of Shade Enclave to trigger a process by which all existence would end and the Multiverse would become literally nothing/emptiness. When the good gods learn of Shar's conspiracy, several of them led by Lathander banded together to defeat her plans. It would be impossible for anyone even remotely plugged into social life in the Realms to have not heard of these events.
Side note: If anyone here has an interest in exploring FR novels, I very strongly recommend anything written by Paul Kemp, and especially his Erevis Cale novels including of course The Twilight War trilogy.
