...The Planet of Titans (tele-)movie project study model.
And while I'm nitpicking:
Perhaps this may be why K’t’inga, Vor’cha, and Negh’Var were adopted for naming Klingon ship classes post-TOS, to help distinguish them.
...That is, Starfleet adopted those because for the first time in its history, it actually had authentic knowledge of such names, perhaps?
A bit like how the Soviet Navy had a "Kara class" in NATO communications, even though there was no ship named
Kara in the Soviet fleet; NATO had pulled that designation out of its ass, applying a vaguely pseudo-Russian name beginning with K for Cruiser.
Although it wouldn't have helped had NATO known that the class ship was named
Nikolayev, because this wasn't "Nikolayev Class", either. Soviets didn't use class names like that: the cruisers (which weren't even cruisers, but Large ASW Ships) were of the Berkut B type instead.
So quite possibly Starfleet of the 24th century would know that the first of the big ships they encountered in 2361 was named
Vor'cha (because Commodore Enwright had been at the launch and gotten the honorary keg of bloodwine), and would call the type accordingly - while Starfleet of the 23rd century would have no way of knowing that the first of the battle cruisers that plagued it from 2271 on had been named
K't'inga (as the agents sent to spy on the project were all gruesomely executed after, during or before the interrogations), but would learn this later and retroactively would stop calling the type D7c or whatever.
Which leaves open the question of where the D designations originated. We hear Klingons discuss the D5 with Klingons in DS9 "Once More Unto the Breach", but that's after the Universal Translator has been listening to such tall tales for two centuries straight. We also hear Klingons introduce the apparently all-new D7 to Klingons in DSC "Point of Light", which is before the Federation UT has enjoyed much access to Klingon dealings - but after the date in "Choose Your Pain" where Starfleet was first heard using the D7 designation. And we hear of T'Pol identifying the D5 battle cruiser in ENT "Judgment", at which point the Vulcans are already intimately familiar with the Klingons, but also with humans whose quaint practices T'Pol is often heard accommodating.
So are the D designations indigenous Klingon ones? Or actually Vulcan ones, retroactively applied to Klingon discussions via the UT in our TV sets? Or a human invention, likewise retrofitted? We really can't tell.
Case in point, the smaller B’rel class is a scout BoP that carries a crew of 6-12 and known to exist by the 2360s, while the larger K’vort class is a cruiser BoP that allegedly carries a crew of 1500 and known to exist by the 2370s.
The only time we hear the name
B'Rel is in "Rascals", where it applies to the gigantic ships that defeat the E-D hands down. These are reused VFX from the War Timeline of "Yesterday's
Enterprise" where the folks of that other timeline called them the
K'Vort class.
This leaves us free to invent names for both the scout with a dozen crew from ST3:TSfS, and for the bigger
Rotarran-style ship from DS9. That is, we can call them anything
but "the
B'Rel class" because that name is already taken!
The DSC era Klingon ships all seem to be unique in design – the Sarcophagus (T’Kuvma’s ship), the cleave ship (called Na’Qjej-class), the Chargh class battle cruiser, the Qugh class destroyer, and the M’Chla BoP – which is reflective of how diverse the Klingons look in appearance as well.
Which is a storytelling point of sorts, too: the Klingons are disunited. We may even assume they never bothered to send actual warships to T'Kumva's silly Kahless Konvention, but appeared in their private yachts or trading vessels or whatnot instead. Save for Kol, whose bellicose stance is well established (even if he doesn't want to share in T'Kumva's war), and whose victorious fleet later is shown to feature the same
Qughs that were present at the Binaries. Although of course everybody flies the BoP of the day in addition.
And outside of L'Rell's ship, they don't seem to have any designations related to D4, D5, D12, etc. Or maybe they just weren't mentioned, IDK.
Certainly there was a total failure to mention any on screen, yes.
But in-universe, it would be pretty easy to claim that L'Rell's cool prison ship was a typical example of the craft of the House of Mo'Kai, and emitted a false signature that made Federation computers variously mistake her for a D7 battle cruiser or a bird of prey. Or for a harmless freighter for that matter.
And I think that D4 concept for ENT was reused as a Klingon Warbird for the Kelvin movies,
upon further review.
The artist himself seems to argue this is the case, yes, even if the design evolved a bit in between. That is, Jaeger at the Memory Alpha page is said to have "followed the lines" of the Eaves original. And obviously the girderwork was lost but the extra guns and the "forward-leaning" stance of the bow and the engines retained.
Timo Saloniemi