NX class star ships

[Kotik]

I've been trying to find some more information on the NX class ships. It is obvious from the series that they are named in the same fashion as NASA's space shuttles, so the following order would make sense

NX-01 Enterprise
NX-02 Columbia
NX-03 Challenger
NX-04 Discovery
NX-05 Atlantis
NX-06 Endeavour

Is there anywere established how many NX-ships were built? My current work on a story is heading towards the time of the Earth-Romulan war, so I would be interested in collecting some info on that without relying on facts from the hideous AU episodes like 'in a mirror, darkly'.

Cheers, Kotik

[Kevin Thomas Riley]

No, it isn't established anywhere in canon how many "NX-Class" ships were built. So you can do whatever suits you, and the number of space shuttles would be a good start.