No, I'm saying that the Cardassians probably forced whoever the Bajoran Government was at the time into formalizing the annexation (disruptor to the head negotiation) so it would all be legal under whatever standard Galactic Law is in those circumstances to prevent outsiders from intervening.
And there would be no proof that it was under duress except from those whom would be written off as terrorists, knowing how the Cardassians are with puppet governing.
So the Feds couldn't just go in and say they conquered them without violating Galactic law, since Bajor was legally signed over to Cardassia.
There's some other realpolitik at hand here too, since the Romulans and Klingons also have enslaved worlds in less legally binding manners and the liberation of Bajor would make them nervous about the Feds future intentions towards THEIR conquests which had less legitimacy.
Again, no Galactic Law worth anything would allow annexation by force just because there's a treaty. ANY conquered country has to sign a surrender which involves turning over territory to the conqueror, but that doesn't mean it's legal. You're saying if the UFP knew a Cardassian fleet had crossed into the Bajoran sector, started landing troops in the capital, etc. that they couldn't lift a finger once an annexation treaty was signed? That's ludicrous. That's an interpretation of the "law" which would clearly favor any aggressor.
Could you imagine if that were true? The Cardassians, Romulans, etc. would just be like "great, let's go conquering away, once we make the poor saps we've conquered sign something called a "treaty of annexation" the Federation can't interfere!"