For sake of argument, I could accept "Star Ship Class" as the official starship class nomenclature of the Enterprise and her sister-ships in TOS, but there are a few major hurdles to clear:
1: Kirk said "there are only twelve like it in the fleet" obviously implying starships like the Enterprise.
While "Tomorrow Is Yesterday" is the second time in TOS the United Earth Space Probe Agency is mentioned, Kirk may have been cautious and referred only to the 12 starships of the 17th design to which the
Enterprise belongs.
And he didn't say "there are only twelve starships".
2: Judging from the list of starship names I compiled upthread, it seems very strange indeed that a Federation of multiple worlds and species would have only a very limited pool of starships, all with Earth-derived names.
The list may not be complete as we are only aware of the 16th and 17th design (and one 18th design) starships that were on the starship status list (only candidates requiring upgrades?) in "Court-Martial".
I believe the biggest TOS argument against "12 starships only" comes from "The Doomsday-Machine". Commodore Decker comments that the maw of the planet killer could swallow a dozen (= 12) starships. Why didn't he just say it could swallow all the starships of Starfleet,
if that were the case?
3: This TOS-only-canon approach put TOS in complete isolation. The original Enterprise and her sister-ships would truly be "in the freezer". No Reliant, no Mirandas or other ships loosely related to the Enterprise at all. Just a very small number of "Star Ship Class" vessels and that's it.
Not necessarily for the aforementioned reasons.
4: The only way I can see adhering to this strict orthodoxy of TOS-in-isolation continuity is if you also agree to the strong implication in "Whom Gods Destroy" that the Federation only came into being after the Axanar Peace Mission, in other words, when James T. Kirk was a young man. For a multi-world Federation to have only a dozen or two dozen "Star Ship Class" vessels in her armada, the Federation would still have to be pretty young anyway.
Hmm...the "Vulcan expedition" remark in "Court-Martial" implies the same, but back in the 1970's the "USS" prefix for some older ships had been accepted to indicate a UFP at least 100 years old by the time of Kirk and company.
This is a very interesting exercise in fandom imagination, and could occasionally be useful, but purely academic at best. One could very logically argue that from TAS or TMP forward the entire STAR TREK franchise has become an exercise in concept erosion ultimately resulting in the 2009 movie.


A beautiful and concise summary, IMHO.
TOS had plenty of follies and built-in contradictions anyway.
Rewatching TOS I was rather amazed of the internal consistency and how many episodes referred to events in previous episodes (e.g. Kirk explicitly asked Spock in "By Any Other Name" to perform the same mind meld through the wall he did in "A Taste of Armageddon").
Some of the "contradictions", the way I see it and will continue to promote, are the result of retcon revisionism because later productions (e.g. movies) didn't do proper research (e.g. the Klingon-Romulan attribute chaos in the simulator room in ST II). Sorry, I can't reward bad research at the expense of the original producers ("They didn't know what they were doing") by accepting it as "canon".
I think another "in-universe" clue to allow distinction between the "Enterprise Class" (17th design) and the "Constitution Class" (16th design) might have been hinted earlier in this discussion.
The
USS Defiant (NCC-1764) in
"The Tholian Web" had the identical kind of dedication plaque as the
Enterprise (I will argue that there was no need to cover it up, as the plaque
did contain the essential "Enterprise Starship Class" information

).
In contrast the
USS Exeter (NCC-1672) did not have this kind of dedication plaque in
"The Omega Glory". One could take this as a clue, that dedication plaques were only granted to starships of the 17th design and beyond.
Bob