There was a mid October
DCL cruise that was already being booked that people were notified the ship was being chartered that week. Saw the thread on the DCL board. Don't know if it was for the DVC member cruise or another group wanting to the whole ship. I vaguely remember hearing talk of moving the DVC cruise to October. Didn't check back to see the outcome.
Having a ship in booking, doesn't mean it is immune to being chartered by a group. There is a thread on Cruise Critic, someone booked a Jan NCL cruise and were just called that the ship is being chartered that week. From what I read it sounds like all the major cruise lines do that.