Except that it's been established since TOS: "Metamorphosis" that there is a human colonial presence at Alpha Centauri.
Metamorphosis established that there was some kind of connection between Cochrane and Alpha Centauri, no suggestion of any form of "Human colonial presence" was made.
"Zefram Cochrane of Alpha Centauri" makes it pretty explicit that he lived there for at least part of his life. And there have been numerous other references in Trek over the decades to the system having inhabited planets. Taranallus of Centauri VII in "Requiem for Methuselah," the University of Alpha Centauri in TNG, a character in DS9 said to have been born in the system -- not to mention ENT: "Twilight" explicitly mentioning a human outpost in the system and a couple of other fourth-season ENT episodes referencing a Proxima Colony, presumably at Proxima Centauri. As I already pointed out, the later-season producers of ENT corrected "Terra Nova"'s mistake of ignoring Alpha Centauri. There is no logic in favoring the single isolated case of "Terra Nova" over the numerous other references in Trek canon -- even within ENT itself -- that contradict it. That's like concluding that Captain Kirk's real middle initial is R.
Perhaps Alpha Centauri is a human presence but NOT an Earth colony? Maybe AlphaCent was seeded with life from Earth by the Preservers a long time ago. (I believe some of the novels have gone with this idea - and something about us being unable to detect them until late because they kept all of their communications on shielded hard lines.)
That was a popular fan theory for a while, but I've always found it an absurd and unnecessary one. There is no good reason within Trek canon to doubt that Alpha Centauri was colonized by Zefram Cochrane and others after the invention of warp drive. That is the interpretation that is most consistent with the preponderance of evidence within canon. That is the interpretation that has been taken by the majority of the novels for decades, despite the few novels that went with the more convoluted fan notion of native Centaurian humanoids. There is no reason to throw all that precedent out just because "Terra Nova" made a mistake. Especially since I've already reconciled it in my
Rise of the Federation novels. (Proxima Centauri's gravitational effect would tend to subject Alpha Centauri A and B's planets to frequent cometary bombardments, so I assume they were deemed less suitable colonization targets at first, which was why Terra Nova was chosen for the initial colony despite being farther away. After Terra Nova failed, Cochrane defied the government and founded a colony at Alf Cen anyway. It's an explanation that has the virtue of being grounded in real science.)
Very technically, they would
still be a colony, I guess - but only in the same sense that Native Americans actually discovered the New World. True, but you rarely hear anyone say that, it's always Eric the Red or Columbus or whomever that found it during recorded history.
Not a lot of people would make that claim anymore, at least not in reputable historical scholarship.
(And by the way, Bjarni Herjolfsson was the first European known to have seen the New World, and Leif Eiriksson was the leader of the abortive Vinland colony in Newfoundland. His father Eirik the Red colonized Greenland.)
On the other hand, it's possible that the references regard space stations located in the Alpha Centauri system.
No, there are too many canonical references to planets and cities in the system. Besides, this is Trek. It's not a universe that embraces the idea of populated megastructures or space habitats all that much. By default, it's always assumed that people live on planets.
Or possibly there is a suitable rocky planet but one that might have required generations of large scale terraforming to be habitable. Not suitable therefore for the 2131 colonists.
That's pretty much the explanation I went with in my books, as discussed above -- that it was a less ideal target for settlement than Terra Nova, but still adaptable with sufficient effort.
