Matrix I think, hit it on the head. Gryph also mentioned in another thread that Time Travel is very rarely linear. I also think UF-G alludes to that when Mio shows up; he mentions in inner monologue how incredible it is that Mio traversed a universe veil and some 400 years time difference, as -well- as half the galactic radius, to land a reasonably short distance from Sakura's cabin.