Again, 3 blind mice is what Barrash tried to play on the trombone in Future Imperfect.

Article 14, section 31 of the SF charter, not Federation. It existed in ENT, before the Federation.31 was explicitly not Starfleet though, it’s from section 31 of the federation charter. Which is what’s at the heart of all this really. At least Matalas remembered 31 are the villains. (Though whether that’s their lock up on daystrom is a good question)
Time to dig up exact dialogue. To clear this up one way or another in general.
(...)
SLOAN: We keep a low profile. Works out better that way for all concerned.
(...)
And that is how 31 should've been all the time. Some of the best scenes in the whole franchise.(...)
ODO: That won't be easy. If he's right and Section thirty one has existed since the birth of the Federation, they've learned to cover their tracks very well.
(...)
Gee, it's almost like he's not Tuvok - perhaps a changeling?What really bothers me in this episode are Tuvok's ears. I don't understand how they are not able to make prosthetics as from Voyager era. It looks so different.
