There is a mass of contradictions regarding the Defiant. The SCE ebooks "Interphase" had the Defiant being recovered in 2376, and no changes to the Defiant's systems were noted by the crew of the USS da Vinci. However, this story was published before the ENT episodes, "In a Mirror, Darkly", which saw the Defiant enter the mirror universe and is later expanded on in the Mirror Universe series.
So in short. We don't know.