In the 2.5 Re:coded secret ending, we see the Organization XIII members who were residents of Radiant Garden lying on the floor after being recompleted as people again. We also see Braig, who is not lying on the floor like the rest of them. He presumably woke up before them. (We know this 2.5 secret ending takes place after Re:coded and before Dream Drop Distance because Ienzo is an adult in this cutscene. There is a cutscene in the beginning of Dream Drop Distance that shows Even and Ienzo on the floor turning into Heartless/Nobodies and Ienzo is a little kid in that cutscene, so we know the 2.5 secret ending takes place after Re:coded because we know Ienzo grew up as an adult while he was a Nobody.)
In Dream Drop Distance, we see Xigbar. It is implied that this is actually Braig, not Xigbar and he's just going by the name Xigbar for some reason (most likely because of the Recusant's Sigil in that name). If this is the same recompleted Braig that we saw in the 2.5 Re:coded secret ending, then how come he has long hair again, how come he has gray in his hair again? It would not make sense for him to just all of a sudden change appearance and grow hair that quickly. Is this actually Xigbar and not Braig, and they were just implying that it was Braig just to trick us? If it's Xigbar, then that can either mean that he was brought to the present day from time travel, or that can mean that Young Xehanort turned the recompleted Braig back into a Nobody for some reason (maybe he's stronger as a Nobody?).
Also, do people keep their appearances that they had as Nobodies when they turn back into people, or are they reverted to how they looked before they were turned into Nobodies? This is very unclear. It seems that some parts of them did keep their appearance and some parts of them didn't for some reason. Ienzo, Lea, and Isa aged as Nobodies and kept their ages when they turned back into people. Lea lost the markings under his eyes when he became a person again though for some reason.
From what we know, this is how it is: You are reverted back to how you looked before you became a Nobody, but you keep your age. For example, Lea was reverted to how he looked before he became a Nobody which is why he lost the markings under his eyes, but he still looks older because he kept his age.
There are some people who think that the 2.5 Re:coded secret ending takes place way back in-between BBS and KH1, but that is simply not true as proved above.
There are some people who think that the Xigbar in DDD is actually the recompleted Braig and the Braig in the 2.5 secret ending is the one who's a time traveler. That is simply not true. As stated above, it wouldn't make sense for the Xigbar in DDD to have long hair if he was actually Braig and it wouldn't make sense for the Braig in the 2.5 secret ending to be the time traveler because he's at the spot where he was just recompleted.
So, this is what we know so far and is so far the absolute truth: The Braig in the 2.5 Re:coded secret ending is Braig after he was just recompleted as a person again. The Xigbar we see in Dream Drop Distance is either one of these two things: He's either a time traveling Xigbar that Young Xehanort brought to the present time, or he is the recompleted Braig that Young Xehanort turned back into a Nobody for some reason. It is currently unconfirmed which of these two things is the answer. If he is a time traveling Xigbar, then that means that Xigbar and Braig are both alive and in the present day at the same time. If Braig was turned back into Xigbar, then that means Xigbar is the only one who is alive and in the present day. We also know that when you are recompleted as a person again, you are reverted to how you looked before you became a Nobody, which is why Lea lost the markings under his eyes, and is why Dilan's hairstyle was reverted back to how it was before he became a Nobody, and is why Braig's hair turned shorter again and lost the gray in it. We also know though that you age as a Nobody and you keep your age that you grew to when you turn back into a person.