To add to what Dante said, it's not like SCVI bothers with giving the characters' ages this time either. Unlike the previous games, this one covers a wide swath of time, so their profiles don't place them at any particular age for this game -- because they aren't any particular age for this game.
Right, but the fact that those stories cover a wider swath of time is exactly why the plots of the later games are implicated. Some elements of the story have clearly been shifted around. As to the "they just made Tira older because it made sense for this or that narrative or pragmatic reason" type explanations, that confuses the issue of why they did something with what they did. Maybe if we look behind the curtain, there's an explanation for it (I'm not convinced that keeping her the same size really saved them that much time in constructing the model: I think its more likely that they wanted to introduce essentially the same character everyone was familiar with, but they wanted her in this game because she's a semi popular character, and they just really have zero concern for such a discontinuity). But it really doesn't matter why they did--the fact of the matter is, she's older than she reasonably could be, based on the old continuity, and that's a change to the story (whether it was meant to change the story or was done for technical reasons or just because they weren't particularly concerned about it, inconsequential as it is in the grand scheme of things).
And look, this is Soulcalibur: it's not like anyone would notice if next to none of it fit together correctly, let alone just a few details being out of place here and there. My point is that Crash was correct: in at least some sense, this game pulls from plot elements of SCI, SCII, and SCIII. The majority of the characters may have narratives that fit cleanly into SCI (or SCI and into SCII), but not all of them do. And while I've not committed the details of all of the original "what if" plots of SCI-SCIII to memory at the level you two have, even I--as someone who is disinterested in what they consider a cornball anime plot, but who has nevertheless been playing the games for two and a half decades and thus accumulated a basic understanding of each character's arc, even if I have long since forgotten most of the details (if I ever looked into them to begin with, in those library modes where most of the info was relegated to in the earlier games, as best I can recall)--have noticed some discontinuities. I take you guys at your word, given your more purposeful scrutinizing of all of that lore, that the vast majority of the plot points sourced and re-incorporated into SCVI come from SCI and early SCII. But, for a certainty, at least some of it comes from materials originally presented in SCIII, so when someone says that SCVI covers events from SCI through early SCIII, I'd say that's essentially correct.
In the Game of Pedantic Corrections you either win or you...!!! ....well actually, you won't really die. Come to to think of it you can't reall lose either, or win. In the Game of Pedantic Corrections, we...all become nerds?