Must be Delta Vega Vulcanis.
The novels have named it T'Kuht, also rendered as T'Khut, and sometimes T'Rukh.
Well, "must" is putting it strongly, but I think it makes a lot more sense in this case to favor the DE version. For one thing, there's the general principle that the theatrical release was rushed into theaters with many of its effects, sound design, editing, etc. incomplete, something that should never have been allowed to happen, while the DE was endorsed by Robert Wise as his preferred version of the film. I'm sure not inclined to argue with the guy who made
West Side Story and
The Day the Earth Stood Still.
More specifically, as I said, the live-action plate was clearly shot in daylight -- Spock casts a shadow and even holds up a hand to shield his eyes from the sunlight -- so the decision to replace the originally planned daylight scene with a night scene was simply bizarre. Plus the painting they used is just too fanciful -- the planet in the sky is absurdly big (unless it's shot through an extreme zoom lens from like a mile away from Spock), and the open lava pits would make the environment so uninhabitably hot that Spock would probably burst into flames just kneeling there. Not to mention that the shot was rushed and there's a visible matte misalignment between the planet and the mountains. It has always looked weird and wrong to me and just wasn't very well done. The DE version is based on the concept art for the originally planned version of the matte shot, the one they intended to do before scrapping it for the weird lava-pits-and-giant-planet scene. And it looks better and makes more sense on every level. I see no reason not to prefer it.
Has all of TOS now been superseded by the remastered versions?
Well, that's a meaningless question, because "all" of TOS has not been altered by the remastered versions, only the very brief portions of each episode that contained visual effects. But on the whole, yes, I would rather believe that, for example, Flint's mansion
looked like this than that it was an inexplicably exact duplicate of the Kalar fortress on Rigel VII right down to the landscape and planets in the sky. Obviously a lot of the FX shots in TOS were just meant to be suggestions or approximations of the underlying concepts, the best they could manage with the resources available. TOS-R was able to use more powerful tools to come closer to the original intent. It's not a matter of one being "true" and the other being "false"; they're just different artistic interpretations of an abstract idea.
See above re: "Yesteryear."
In The Enterprise Incident now only have 2 D-7's instead of three, the other being replaced by a BOP?
Which I think was a great idea, as was the Romulan-style paint job on those D-7s. It made it feel more Romulan. The reason they used the D-7s in the original was simply because they'd built this expensive ship model and wanted to get more use out of it, and because they'd misplaced the original Romulan ship miniature. It wasn't a pure, perfect artistic decision, it was a compromise made due to pragmatic limitations. It's part of the overall work now, but I have no problem with the refinement of putting a Romulan ship in the mix as well. Again, it's just a difference of interpretation.
Why can't we accept that it's simply a different version of the same things? A parallel universe with very minor differences. In one, Vulcan has a large co-orbital planet that has at least one moon, in the other, no sister planet. Must the past be overwritten? Isn't there room for more than one interpretation?
Again, see my comments re: "Yesteryear." It's still possible to believe that the companion world exists; it's simply that the depiction of that world presented in the theatrical edition's matte painting was deeply problematical on many levels. "Yesteryear"'s version isn't quite so astronomically or geologically ludicrous, nor as badly designed a painting.