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Lt. Commander
Join Date: Dec 2007
Posts: 120
# 7
02-15-2011, 08:48 AM
Registry numbers in Star Trek, especially later, are notoriously inconsistant (see the Prometheus article for an especially egregious example), and no "system" for how starships are registered that his been mentioned on screen. It's generally thought that ships get their registries in the order they're commissioned, but without confirmation, even that's speculation. However, there are at least three constants regarding Starfleet registries:
  1. The prefix NCC represent a registered starship, while NX represents starships generally considered prototypes. The NX series seen in Enterprise is an exception (the familiar arrangement perhaps adopted later in Starfleet history) and, in theory, most ships labeled NX are eventually changed over to NCC when they enter active service, as per the USS Excelsior (the DS9 Defiant being a notable exception).
  2. With the exception of the Enterprise, no two ships carry the same registry number, even those that carry the name of a predeccessor. As far as I can tell, they don't even carry part of the old registry of their predecessor.
  3. In relation to number 2, the Enterprise is the only ship that carries a letter suffix after its registry (the Yamato being a noted mistake in that regard). The in-universe reason for the Enterprise being the only Federation starship with this distinction is sketchy at best. I have also noted that the Enterprise is the only ship in with the registry number combination "1701," which leads me to believe that registry numbers that end in that combination (i.e. 21701, 61701, etc) are held off for the Enterprise.

So generally speaking, as far as "canon" is concerned, only the Enterprise is given the the distinction of carrying the same registry number as her Constitution-class predecessor (with appropriate suffix), while everyone else is given a brand spanking new registry. As far as the second DS9 Defiant, outside of obvious stock footage, I see no reason why that Defiant would not carry the registry NCC-75633. True, Sisko was given dispensation to rename the ship from Sao Paulo; I don't recall him getting permission to change the registry (and cause a major administrative headache in the process).