I seem to remember, and am prepared to be corrected, that there was an SI that said formations could cross CAS but not join and fly along the airway.
Going back to Sector 9, if traffic is flying along G4D, there is the option of giving an Air Traffic Advisory Service. I'd like to ask any pilots out there a question:
If I gave you this service, what would you be expecting in terms of traffic information and avoiding action?