One secret society that appears to be overlooked, is the stone shamans of Shinovar. We never really hear from them directly, only the things that Szeth thinks about them, especially after his encounter with Kaladin on the Shattered Plains. Szeth gives us insight into the stone shamans that leads us to suspect that they remember a great deal about the KR. For one, Szeth menions that he went to Urithiru shortly after being made truthless. This means that they have known where it was located all along.