We all know how No.6 hated being called No.6, or known by his number. The Colonel said of him in Many Happy Returns "You're a stubborn fellow Number Six!" To which he replied "James, you call me that again, and you're liable for a bout in hospital." So why didn't the Colonel use No.6's name in the first place? Better still, why didn't No.6 say to the Colonel "Please call me by my name."