Short haul and particularly UK domestic routes have very short booking lead times .It is inconceivable that a large number of flights in June i.e. Nearly 6 months away are fully booked...one date because of a large group maybe but not a series of flights.The flights are either not operating or have been closed out possibly pending a decision to cancel or not.
If fully booked it would mean putting on additional flights but somehow doubt that is a scenario. Agree that it seems that FB is not most accurate of info being put forward.