I've revised a few of my theories since previously posting in the Starbase 11 chart thread. Resurrecting this thread because I honestly believe there's something new I can add....and still tie in to modern canon.
If one accepts other beta-canon versions of the Four Years War, in place of Discovery’s conveniently ADHD short, victorious war, the circumstance provides an explanation for the variant/oddball NCC's assigned to the Constitution class. Based in canon as much as possible, but incorporating other fanon I like, integrated into my own headcanon, and thus no more “authoritative” than that. Feel free to agree or disagree.
While I regard Franz Joseph’s designs as (head)canonical, and his intents on track, I do NOT regard his specific class listings as canonical. He had the right idea for class sizes, and the right names, but ordering and numbering? Too many cooks stirring the broth, and his vision got outcompeted.
Whenever possible, Fleet Construction Command (as evidenced by Franz Joseph's and FASA’s numbering) will allocate a block of consecutive NCC's to a class (or subclass, aka “flight” of a class) approved for building. A lot of them ended up getting reshuffled because the Klingon D-6 and the Four Years War had totally obsoleted a large number of unbuilt vessels before the keels had been laid. However, even the very act of allocating a block of numbers can tip off an enemy power that a new class is coming; all it takes is a spy in a low-level secretarial position somewhere in the military industrial complex’s bureaucracy to find that out. The Klingon High Command had placed such agents. Federation counterintelligence realized that the Klingons were getting better info, but couldn't pin down the exact source, not quickly enough to matter.
While unable to conceal the planned existence of the new heavy cruisers, measures could be (and were) taken to obfuscate the number of new starships within the class. To this end, unused NCC's from other, earlier classes were used to disguise the fact that instead of merely accelerating construction of the first ten “New Starships”, nearly double that number were being built! Hence USS Eagle (NCC-956), Constellation (NCC-1017), Intrepid (NCC-1631), among others.
Given other canonical numbers, it almost seems as if, at NCC-1700, Constitution is a fairly late build of the class, rather than the first! This implies a predecessor class (and I don’t mean Discovery’s Sombra-class), which I have seen someone else (way back in the dawn of this thread) call Magna Carta class. I agree, but give it a different name. On a related note, how did these vessels end up with the utterly generic tag “Starship-class”? Simple. A Universal Translator glitch. Evolving technology is NEVER perfect, especially the earlier versions!
So I say, the class vessel of this new heavy cruiser class, the lowest numbered vessel of the official NCC allocation, was USS Aster, NCC-1650. Instead of treating the name as a loan-word from Latin, and passing it verbatim, the Universal Translator “autocorrected” it to “star”; hence the class became known, particularly outside of StarFleet, as literally the Star ship class. The appearance of these vessels are exactly as USS Enterprise was under Pike’s command in TOS “The Cage”.
The Asters are intended to be a more robust version of the Sombras, somewhat slower but much more able to stand and fight. The Bussard Collectors do not glow because they are covered with armored caps, rather like the Pacific 201 design, a wartime modification to prevent down-the-tube shots from destroying ships outright. The antennae projecting from the nacelle domes are Tesla Atomic Attractors, an active deuterium collection system to counter the restriction of passive collection caused by the armor. Collected atoms, once attracted, slide down the dome and wick into the nacelle through a barely visible notch encircling the nacelle at the base of the dome.
I’m also figuring that several of the ships immediately following Aster (NCC’s 1651-1675) were destroyed, unfinished and uncommissioned, in construction yards by Klingon raids, if not during the war itself.
So, what IS the USS Constitution? Basically, an Aster subclass, Flight II. The first Connies were supposed to have been built to the new specification, but due to production delays, the first few (17XX-series such as Connie herself, and Enterprise) had to be finished out and placed in service with Aster nacelles, bridge modules, etc. With the intended upgrades known to the designers and planned for, Constitution-spec assemblies would be drop-in replacements, as opposed to the extensive refit process an older Aster would have to undergo to reach the same performance levels. While several notable Asters (such as Constellation NCC-1017 and Excalibur NCC 1664) received this upgrade, Fleet Logistics Command found that it was almost faster (and far less futzy) to simply mothball or scrap Asters and build new Connies from the ground up; those that did receive the refit, were considered to be, with the first Connies, the “original twelve”. I'm still on the fence as to which of the 14 Known Names to count as Originals. Meaning, at the moment of Kirk’s comment, ships upgraded to Constitution-spec rather than Aster-spec. Not by ANY stretch of the imagination the total and absolute extent of Starfleet!
