Ah - so you deleted the entire dataset hierarchy? That includes the snapshots, unfortunately.
Actually, the data was in two places, one, a ZFS dataset defined in Truenas, the other, data stored in the jail. I have the Truenas datasets, I don't have the jail data because I deleted the jail, and that's what I'm missing. I have plugin snapshots, but I don't believe that will recover a blown-away jail without the jail data the snapshots are tied to. Am I missing something?
This was a case of a Nextcloud plugin that used both jail data, and external data (Trunas datasets), which was defined external to the jail in Truenas.