Keep in mind that they're not entirely forgotten in Southern Magnamund (Grey Star winds up in a prison cell with a Shianti priest, after all), so SOME lore still exists, as distorted as it might be (people seeing them as gods, etc).
I'd say in Northern Magnamund, there's probably not much known save by certain groups, like the Sages of Varetta - after all, even the Magician's Guild refers to the Shianti who once dwelled in Kalte (or the Graveyard near Holmgard) as the Ancients. Even the NAME Shianti has been apparently forgotten there...