Okay, I've had this idea percolating in the Trekkish corners of my brain for a little while. I'm sharing it now before this grind/whine noise in the right ear distracts me completely: the
Constitution class of starships has been in service since at least two decades before
Enterprise NCC-1701 was commissioned.
You want evidence. That's good.
What I have is the confirmed - in the episodes and movies as shown on TV and in the cinema and via subscription-streaming - registry numbers of the Federation starships we know for certain to be of that class.
I'm sourcing this from Memory Alpha...NCC-956 USS Eagle
NCC-1017 USS Constellation
NCC-1631 USS Intrepid
NCC-1659 USS Potemkin
NCC-1664 USS Excalibur
NCC-1672 USS Exeter
NCC-1700 (Unknown)
NCC-1701 USS Enterprise
NCC-1703 USS Hood
NCC-1707 (Unknown)
NCC-1709 USS Lexington
NCC-1764 USS Defiant
NCC-1856 USS Emden
NCC-1895 USS Endeavour
NCC-2014 USS Korolev
NCC-2048 USS Ahwahnee
I discount
Greg Jein's theory - "The Case of Jonathan Doe Starship" - that all starships docked at Starbase 10 during Kirk's court-martial re: the death of Benjamin Finney were Constitution-class. The odds of such a happenstance are too small for me to consider. And thanks to
Star Trek: Discovery in general and the work of designer John Eaves in particular, we now have other options for the registries listed there.
I also prefer to assume - based on over 50 years' worth of evidence from the various series - that Federation Starfleet ship registry numbers are issued on a chronological basis, without interruption.
Up until now, I chose to believe that (1) the
Constitution herself was NCC-1700, and that all ships with registry numbers prior to hers were salvaged from previous starship classes. No longer.
It may still well be that NCC-1700 belongs to
a Starship Constitution...but she need not be either the first of her name or of her starship class. Not with six other starships of the class commissioned before her.
Kirk's claim of "twelve like her in the fleet"? Depends on your point of view. Going by registry numbers as confirmed, I'm willing to hazard a guess of at least three, perhaps as many as five production batches of ships. Kirk's twelve ships would certainly count as one of those three to five batches.
A lot of us have some investment in the mythology as established before DSC. I certainly did. I bought books and deck plan sets and stuff - not all of it officially licensed, but that's okay, because multiversal theory allows us to keep enjoying what we've bought as if it were official in some other version of Starfleet, somewhere in that multiverse.
Anyway, there it is. I think I wrote it out coherently enough. Fellow Treknology fans are welcome to debate whatever parts they like.