It won't be me flying, I'm strictly SLF down the back with a good book and a comfy pillow.
I've just spent the morning reading every document I could find.
The info is quite specific when you land at Norfolk, Coccus, Christmas Island they are the same. Pretty standard international ops if comming from a foreign country.
But nowhere, and I mean nowhere, does it explicitly say that you have to depart the mainland for NLK from a designated international airport, or return there. In fact the regs read that from 1July 16, Norfolk become a First Point of Entry to Australia if coming from say the USA. I gather you clear customs now for Oz in Norfolk on a transpacific ferry. It does not say you have to clear Aqis on return to the mainland. Aqis formalities are only doen at Norfolk, Coccus, Christmas islands inbound.
But am open to being proved wrong if somone can provide a reference.