The Use of the Smith Family's Bloodline

Irving gleaned a substantial amount of useful information from Elder Seville's mutterings.

First and foremost, the most valuable piece of information was that Elder Seville did not obtain the details about the Smith family's hidden treasure from Joseph. Instead, he got the information from an ancient tome. Secondly, Elder Seville initially did not believe the contents recorded in the ancient tome. He only started believing it recently, possibly due to information provided by Joseph or perhaps a tip from someone within the Night Blades.