I guess the only thing to add here is that we probably agree the letter part of the registry would be an utter waste of paint unless there were alternatives to NCC. That is, yes, we know that there exist registries such as NAR-something and NSP-something etc., and yes, we have good reason to think that these correspond to the operating organization of the vessel in question, leaving NCC the specific "Starfleet operates me" symbol. But this further carries the connotation that a pairing of letter identifier and string of numbers would be unique, so it's possible that the strings of numbers alone need not be unique.
See what I mean? There may exist both NCC-12345 and NAR-12345 within the same system, these being separate ships. But OTOH, there might not.
If, for clarity, a registry already used for a NCC vessel never gets used for a NAR or NSP one, then the number of actual Starfleet ships goes way down. Starfleet might be the leading "consumer of registries", but it might also come a distant second to some other organization, at least at certain periods of UFP history.
Do we have any canonical cases of the same number being used with two different letter prefices?
You make a very good point as usual - and set up an interesting related question: does the number belong to the vehicle, or is it reassignable? Would NCC-1701 become NAR-1701 or NSP-1701 if she was sold off to another division? How often, if ever, are naval registry numbers or aircraft registry numbers moved from one craft to another in the real world?
Unless memory fails me, the second DS9 Defiant
is the only clear case of a registry number even possibly being transferred/changed that we have. Of course, the Defiant
is also made more murky by conflicting evidence as to whether or not she actually retained her original registry number. Sisko's line says Starfleet gave permission to change the name, but doesn't specifically say whether they gave permission to change the registry.
-A is also a possible case, since popular opinion has it that she was another ship to start with, be it Yorktown
or whatever your personal canon might suggest. What happened to that ship's registry? Was it retired, with another planned for construction, or was it transferred to another vessel?
Starfleet seems to be of the opinion that registries should stick with their original starships more often than not, if only for the sake of administrative clarity. (I certainly would hate culling through records trying to guess which Enterprise
was being referenced if they were all NCC-1701.) Barring further evidence as to whether they are as unique as serial/VIN numbers, I think we are safe assuming that registry numbers are not
usually transferred between ships nor are they retained when a vessel is renamed/reprovisioned. So different letter prefixes having a unique registry range independent of each other works for me.
Regarding ships and sectors, it did seem to work out nicely to guess on the size of the Federation and the size of sectors to get 2,500 ships. It would be interesting to compute what a proportionally smaller Federation in the 23rd century would yield in terms of ship count, if it is Starfleet protocol to have at least one patrol ship per sector, that is.
As an aside, I always assumed sectors were divided into quadrants somehow. This would make the whole "she's the only ship in the quadrant" work out better. Plus, the Federation is probably divided into quadrants, too...