Last time BA put out something like this, it was filled with more holes than a block of swiss cheese. I would take it with a *serious* grain of salt. The rule exists out of fairness. It would otherwise seriously impede the choices of people who are originating in Perth if they want to go to NZ, or those in NZ if they want to visit Perth.

89N . EXCEPTION - NO RESTRICTION BETWEEN SYD-PER FOR
90N . PASSENGERS ORIGINATING PER OR NEW ZEALAND WHEN
91N . IN CONJUNCTION WITH TRAVEL TO/FROM AFRICA