I always use this method for booking from SYD.
Unfortunately, it is largely useless as H is (I believe) 21 advance and even if the flight is showing J9....it is almost always J0 the day before the flight.
As for C.....I can't remember the last time I saw C availability less then 7 days out.

On the other hand, I seldom book with United or the soon to be out of SYD NZ. Even with their larger J cabins, there is only a very slim chance of an upgrade based solely on *G status. Any no-show on AC pretty much gives me the seat..unless of course Ferrari is around

Obviously, this is not a good route for this kind of strategy.

MCM.