I believe there's a one-off line in DS9: Avatar that says either the Defiant crew salvaged the cloak from the destroyed ship and the Romulans allowed them to keep it or that the Romulans gave the the UFP another cloaking device for the Sao Palo/Defiant because of the war and then voted to let them keep it afterward.
I don't see how they could have salvaged it - the Dominion took the Chin'toka System in the aftermath of (and as a result of) the battle, so how could they have retrieved any systems from the wreckage? I must say I've forgotten about the line you mention - in fact, that always bothered me, in that I couldn't remember why on Ear- on Bajor - the second Defiant
had a cloak in the relaunch.
The Romulan ambassador must have been rather annoyed with them.
"The agreement says only the Defiant
can have a cloaking device. Well, we've painted over this new ship and called it Defiant
, so it counts! It's even a Defiant
-class! Gimme, gimme, gimme!"