Talking about those Datas, I don't remember Sora finding them in this game. Did he ? (might have missed it since I haven't played it !)
I can't say much about it during the actual game, but in the second part of the ending Riku is inside Sora's heart and after he answered the questions asked by Roxas, Ventus and Xion, the data Ansem had hidden in Sora manifested as a "Data-Ansem" and Riku has a long talk with him.
I guess that this is the data, but that part still isn't translated.
Indeed, but unlike the others, he's the only one directly tied to Xehanort (he is the reason Xehanort was able to time travel, the reason the organization 13 was created), and we have no idea about what happened to him, and what/where he is now. Unlike Ven Aqua and Roxas (I could care less about Xion seriously, but I guess she's in Roxas so..). They all have "complicated" stories and the way to save all of them is not an easy thing, for sure.
But while being the case for Terra, we also know NOTHING. And I just find it odd, for the guy who became the "vessel" of Xehanort, who started the whole KH 1 and 2 stories, to never be mentionned. But I blame Nomura for saying after BBS's release that Terra's story had more to it, and that the control "share" was a key component of the story that would be told in the future game.
Bullshit or KH 3 (or BBSv2) I guess. I just hoped it would have a little more info in 3D. At least we saw Terranort refused to call himself Xehanort and picked "Ansem" instead...
EDIT: Ok, now to this part.
While I agree that he is the one "most directly tied to Xehanort", I don't get why Terra should be the one responsible for Ansem SoD being able to time-travel.
Creating the Organisation was Xemnas' and Xigbar's idea to further MX's master plan, I also don't really see what Terra has to do with it.
That we have absolutely no idea of his current status and what happened to him throughout the 10 years is correct, but the latter we in all honesty also don't know for Aqua.
Roxas and Xion should be both sleeping in pain insde Sora, just like Ventus' broken heart is since 10 years ago while Naminé should do the same inside Kairi.
The way to save them is apparently tied to Ansem's data if we can trust Nomura's words, which is why it wonders me that the second part of the normal ending is still not translated.
That we know yet "nothing" about Terra's situation may be intentional though, and I actually doubt that he had much of a real influence on things that happened, as Terra is not the type to go along with horrendous crimes like Xehanort does.
I know he said he would do anything to help his beloved friends Aqua and Ventus, but I doubt he'll become a mass murderer destoying entire worlds for it.
Nomura DID say that how the memories, hearts and powers of Terra/Eraqus and Xehanort were divided between Ansem SoD and Xemnas will be important, but it doesn't have to mean it's actually highly elaborated upon in DDD.
Still, I won't make any definitive statements yet anyways, as we have no official full translation yet and also no new Nomura-interviews regarding DDD as a whole.
Also, if you look closely, I don't think that on "something of Terra might be in Riku" was put any emphasis as well yet.
(Do I sense a pattern here?) lol.