Xemnas says in both "the four of you are going to reveal_____." The particulars are vague in each instance, but outright saying it's a mistranslation at this point is spreading disinformation. Demyx and Luxord's pasts haven't been made clear, but there's more than one way of being ancient, and there's more than one way to have a sleeping "legacy." The Dandelions fates aren't yet made totally clear, and further, they are not the only "ancient" beings, because the Master's childhood Keyblade War was even farther in the past. We don't have enough information.
Mmm, you got me there. But despite that, the line is still mistranslated; the 'legacy' part, that is. There's no word that means 'legacy' in it, and that part caused some confusion. 'Legacy' is something that is passed down generations...but that doesn't make sense considering Marluxia and Larxene.
I also found this segment from the KHIII Ultimania:
In KH3, Xemnas explains that the reason ex-Organization members No. 9-12 were invited to the Organization was to search for (the ancient Keyblade wielders). The reason they were called together was because Xehanort thought that the ancient Keyblade wielders held the secret to the past fight of light and darkness—the Keyblade War.
Xehanort was trying to find out about the second
Keyblade War, not the first one. So it wouldn't be reasonable for him to get someone from the Master's childhood.
(And one thing I forgot was Demyx's character file, which hinted at a connection between Demyx and the Master)
The first point is irrelevant, because Luxord could have gone through the same trajectory as Lauriam and Elrena did, and therefore is about the same age as them. The second one is false, because the same trick that allowed the Dandelions to transfer to other worldlines after the Keyblade War mentioned in Luxu's secret report cannot be the pods. The union leaders didn't know the function of the pods until Maleficent told it to Lauriam. It seems clear that they found an alternative way out.
Ah right! (Those Luxu Secret Reports keep tripping me up. As of right now, they don't even make sense lol)
But...something doesn't fit. Wouldn't Xigbar/Luxu recognize him if he were a Dandelion (he's literally been watching them this whole time after all)? If he were a Dandelion, why would Luxu question his identity in Re:Mind?? It doesn't make sense.