I can't recall how many of the original NX's survived. I know 01 and 02 are accounted for and two or three of the others were destroyed.
How many were built during the war, and did production continue in peacetime ? There must be a few left to refit...
The Romulan War
novels established that NX-class (and Intrepid
-class) production halted in favor of the easier-to-build Daedalus
class, and systematically trashed most of the NX fleet. We know Columbia
was lost in Destiny
, and Beneath the Raptor's Wing
blew up Challenger, Discovery
, and Atlantis
was crippled and decommissioned. Indistinguishable from Magic
introduced an NX-07 Intrepid
(implying the canonical Intrepid
, namesake of its class, was destroyed during the war), but it was lost shortly after the UFP's founding. That leaves only Endeavour
, which was severely damaged in BTRW but not destroyed.
Now that the war's over, of course, there's no reason to continue that Daedalus