Good point on familiarity with "spotted" Trills. The TNG Trill looked very different to Dax after all.
As for Torias, what makes us think that he would have been in Starfleet? Merely the fact that he did space service of some sort, flew shuttles, fought battles? That need not have involved Starfleet in any way.
specifically references Torias as being in Starfleet:
Torias Dax is the first Dax host to join Starfleet serving as a shuttle test pilot. He is piloting a new Starfleet shuttle when it suffers a catastrophic system failure and crashes, costing Torias his life. After Torias' death, official Trill records indicate that Dax is held in stasis for six months and is then transplanted into Curzon (Equilibrium DS9 episode); this is actually a cover-up by the Trill government since Dax's next host is Joran, a psychopath and a murderer.
...and we can assume Dax has TOS-era Starfleet experience from her fetishistising of the tricorders of the time, so this presumably came from Torias.