Okay, something has been nagging at me so I decided to go back and check.
In The Making of Star Trek there are reprints of memos dating around early August, 1967 wherein they are discussion proposed names for starships. The thinking behind these suggestions are to "establish the names of the 12 ships of the Enterprise Starship Class." The idea conveyed here seems to be implying sister ships like the Enterprise but not necessarily of the Enterprise-class.
Timo suggested the same some while ago in another thread. I agree that this is a possibility, but
Bob Justman would probably not have used the term "Enterprise Starship Class" had
"Constitution Class" been established behind the scenes (he would have rather said "12 ships like the Enterprise
to avoid confusion, nitpicky as he was).
Later it says "The Enterprise is a member of the Starship Class (there are twelve of them). Registry Number NCC-1701."
Throughout the text I cannot find any definitive reference to "Enterprise-class starship."
Your above quote comes from the lower half page 203 (Chapter 3 - Mission and Men) and 9 lines further down it reads
"The Enterprise-class starships have been in existence for about forty years..."
Since Jein mentioned the "forty years" in his treatise to suggest that Valiant
couldn't be a starship like the Enterprise because it was fifty years old ("A Taste of Armageddon"), he obviously and conveniently ignored to elaborate on "Enterprise-class starship".
Probably it was cognitive dissonance
, however I wasn't aware that it was contagious.
So was the Defiant a replacement for a previously lost ship or was it there all along as one of the twelve? One could argue the fourteen names were meant as a pool to draw from yet no one was really held to it if they had a another suggestion, which seems the case when they used Defiant in "The Tholian Web."
was NCC-1664 (apparently nobody wonders why I wonder whether it's supposedly "1664" on that chart or "1864") it's possible that the Defiant
inherited the two-digit contact code and became NCC-1764.
was considered lost and/or destroyed it's possible Reliant
inherited the two-digit contact code and became NCC-1864.
But later another Valiant is mentioned as being lost fifty years prior in "A Taste Of Armageddon." Could this Valiant be of the Starship Class or is it yet again another older ship that predates the existence of the Starship Class? I never got the impression the Starship Class vessels were easily fifty years old. At the time of the Kirk era the impression I get is the ships are no more than maybe twenty-five years old. If so then if there is indeed a Valiant among the Starship Class then I'm assuming it's still out there in operation as it's not the one referenced as destroyed at Eminiar 7.
Since the much older Archon
was a "starship" the second Valiant
could have qualified as a starship, too (for its time and era).
Jein assumed the producers to be in error when deciding for Valiant
to be a starship like the Enterprise,
too. But, of course, just as the Eminiar 7 Valiant
was named after the UESPA Valiant,
there could have been a starship like the Enterprise
bearing the same name (and not to mention later ships) that had been equally destroyed by the time he producers made up the list.
Add another little tidbit. FJ gave the Valiant the registry NCC-1708 and 1708 is on Stone's wall chart.
FJ gave the Intrepid
the registry NCC-1708 (which is not
on the starship status chart) and Valiant
the registry NCC-1709 (which is on this chart).
The Starship Class could be a classification that Starfleet has used for quite some time denoting their best-of-the-best ships, but of course as time and progress marches forward newer and more advanced versions could be introduced and the Enterprise is (at the time of TOS) among the newest, the elite twelve of which we really don't know all the names.
Obviously something we can agree on.