My impression had always been that post-TOS the concept of alphabetic classes (suggested in "The Menagerie I") had never been pursued.
Well, as you point out Starfleet was still using old Class J training vessels in TOS, but that isn't definite proof that the letter system had been completely phased out by TOS.
But whatever the "N" in "NCC" stands for, it stands to reason that the "N" in "NX" is the same and part of the registry, not of a class.
Possibly, but without further context (which ENT failed to provide), we don't know for sure.
The model designers were thinking of some of the other Starfleet ships as the NV-class and the like.
No, that's a myth, based on a model kit of the "Intrepid" type which was labeled with "NV-01." Neither of the pre-NX-01 Earth Starfleet vessel types were given registry numbers or class names, nor did the designers of said CGI models bother with that sort of background info.
^ IIRC, the Intrepid model had a registry number that started with "NC" as did the Sarajevo class from "Daedalus."
The "NC" comes from concept art of the Sarajevo from John Eaves. Unfortunately Eaves has the penchant for giving weird markings on his concept art (i.e., "NCC-1254" for a ship design from the late TNG era), so anything he did on his concept art isn't really valid, and it didn't show up on the final CGI model anyway.
I don't recall any of the other models having any names or numbers on them. At least I don't recall seen any from Doug Drexler's old site.
The Starfleet ships didn't. They didn't even have official class names, the first type being called the "warp delta" and the second type (the Intrepid-type) being called the "half-saucer" or some such thing. Some of the ECS freighters might have had registries though. The ECS Fortunate has the number ECS2801 on its hull, which
could be a registry.
I'm really not getting all the dick-waggling you guys are doing about this subject. Scotty wanted to see the TOS Enterprise bridge. He specifically told the computer that he didn't want to see the bridges of the A, B, C, or D, and he gave the TOS ship's registry number. So the computer showed him the TOS ship. What's to argue about here? is it about the "five Federation starships" comment? That would be the Ent-nil, the A, B, C, and D. Again, what's the argument?