Humanity made first contact with the Banu in Davien, which is at least five jumps from Banu territory according to the Starmap. The Banu in question was not an explorer, but a fugitive, which implies that he knew of those systems already, which in turn implies that other Banu knew about them. In fact, we know they must have because of Trise, which lies clear across the Starmap from known Banu space, at least eight jumps by my count, and to make the trip in eight jumps from Geddon would mean going through Terra. In any case, Trise is a long way from Banu space, and what's between the two is mostly UEE space or what's become UEE space. So the question is, if the Banu knew about all these uninhabited systems for so long, why didn't they colonize any of them?