Luthor Harkon said:
Well, in my opinion it depends on when you enter the Schola Progenium. That all Arbitrators (and Commissars btw) are from a Schola Progenium has been always rather clear backgroundwise in my opinion. Regarding the homeworld origin, it depends on when you entered the Schola Progenium (sooner or later). My groups Arbitrator has an Imperial World background as he originally came from an Agri World and was dumped at a Schola Progenium because his father was killed when he was 11 years old. Some are more or less brought after birth to a Schola Progenium (Kindergarten Progenium...?) and those should have the Schola Progenium homeworld origin instead, as they have never seen anything else in their life.