I could be wrong but I'm pretty sure that QF12 LAX to SYD cannot depart until after QF12 from JFK has arrived due to being the same flight number, even though they are different aircraft.
Therefore if the QF12 is delayed from JFK, the QF12 and QF16 on to Australia will both always be delayed due to the above reason for QF12 and because the JFK-LAX aircraft goes on to operate QF16.
