the scene where we see them talking... later on we actually see that scene again and we actually hear xemnas say "sora" so thats why i dont go with this
I found this video to help support sort of what I'm saying. It's when Sora fights Xemnas in Kingdom Hearts Final Mix:
Watch this again (as I'm sure some of us haven't in a while) and listen to what Xemnas says:
YouTube - Kingdom Hearts: Final Mix - Unknown Fight ENGLISH Subs
Notice how he says that "he [Sora] is special too" and "you [Sora] look like him."
He even describes Sora as "incomplete" which doesn't necessarily mean he's referring to Roxas at the time.
See, it's parts like those that get me to think that there's got to be something wrong with what Xemnas is saying.
It's quite possible he could be referring to Vanitas for all we know based on him looking like Sora!
Speaking in canon, when Sora meets Xemnas in FM, Roxas would have been barely born or not born at all (depending on when the boss is fought). This creates a time gap between when you fight Xemnas as Sora and when Xemnas talks with Roxas on the sixth day Roxas is in the Organization.
If the
true motives are revealed in the future as to what Xemnas's intentions were with Kingdom Hearts (in the context of BBS), then we very well might find that he did in fact find Ven and that (between the time he first fights Sora and goes to see Roxas in the RoD) he knows where Ven is.
Or here's another theory:
Xemnas is in fact referring to Vanitas and does in fact tell Roxas that Sora looks "a lot like him" (Roxas). This would make more sense and allow Nomura more room to improvise information concerning some of the past games.
Again, this does clash with current understanding of the series, but if Nomura can say that BBS was before heartless were made and there ended up being heartless, then he can adjust the story from previous parts to tie into this idea as well (unintentionally even).