I wouldn't try going as far as to explain why this was proposed. Separatist sentiment? Yeah, maybe - then again, you could also argue that with the Border Worlds intensively cooperating with Confed after the BL crisis, it would have been highly politically desirable to continue with a unified system of designations, to show how everyone's gotten over the troubles. All we know is that, as far as the writers behind these "did you know" thingies are concerned (and unfortunately just the writers, because it's not officially published, gosh darn it!), for unknown reasons the Border Worlds chose to go with a different system. It's cool, I'll run with it, but I won't try to explain it unless I have to .