If any of this is already confirmed or has been discussed at length already, feel free to ignore, I'm not great at searching for topics....
In WaT, there were a couple references to Taln's past: That he tried to kill Cultivation and he had a powerful weapon but lost it. (I don't have exact references, forgive me.)
Is it possible that Taln acquired Nightblood to use against Cultivation (Vasher is NOT a Shard fan, and I could see him doing such a thing)? Then he lost it while failing to complete the job, which is how the NightWatcher had it to offer it to Dalinar in the Oathbringer flashback?
