Sorry, not really along those lines.... but
Did Seven come up with a pip of an insight even while she was reaching the nadir of her cognitive overload in the Voyager Conspiracy? The direct rejoinders to her blatherings about the tri-cobalt detonation at the array, danced around addressing the issue of Tuvok's delivery yield determination.
Whether or not their use had been proscribed at the time of Voyager's mission (it seems unclear when the Second Accords went into effect, per a number of different sources), why would Voyager have had them in their inventory at all? Given the assignment, there would not appear to be any reasonable justification.
I suppose if not yet banned, the weapon might simply have been a default bauble in the armory of this class that was a shiny additon to the Federation's stable.