Are they separated from the Orbit Guard?
The IGBV aren’t part of the Watch Constabulary or other policing organizations; they’re exactly what the name implies, the border guard. They’re the ones who stand on the mostly-metaphorical wall[1] and declare “Civilization, this side. Everything else… over there,” with the necessary means to back it up.
They also run the inplacement/outplacement processes at border crossings, sorting folks to the appropriate sides of the wall like immigration-focused Maxwell’s Daemons.
The Empire doesn’t have a lot of land borders these days, but not a lot isn’t the same thing as none. ↩︎
The reply establishes that the IGBV is separate from the Watch, but doesn’t say whether it’s organizationally separate from the Orbit Guard. The distinction may be between border duties and orbital defense.