Sounds like it is not full J and the A330 flights MEL-SYD are often sold out in J with WP/SG upgrades that clear the day before .. I've failed to get full J on the A330 for this reason. But really not worth it and often the B737 service in J is better for meal/wine (and how do you use a sleeper seat on hour flight with meal service?). If the ticket is restricted to changes by TA only (and some are for various reasons), then QF can't (no airline can any more thanks to computerization).