Indeed, and first exodus parties disappearing, some to mechanical/technical failure, but that couldn't have been all of them or even most, I would hope. :) Then a second exodus after the TA fell, then people disgusted and fleeing Age of War IS, or Shiro Kurita. And then the aforementioned Star League expansion/possible outposts, that IE couldn't have fully accounted for.
I think there's room for anything, and it was set up that way from the start. Comstar's original handbook/reports were everything as far as they and their various "business" was concerned, so the POV is strong in its sphere of influence, no pun intended, but beyond that they had to have te Explorer Corps, and even that was mostly focused on limited areas of search, ie, Kerensky's trail.