Baggage is a shambles. Even without checking the QF website, my BA issued DONEx ticket shows 3x23kg for SYD-PER but only 2x23kg for subsequent 73H sectors - all ticketed and seated in D.
edited: QF MMB says 2x23kg SYD-PER inspite of BA MMB showing 3x23kg
Prepare for frustration as there is nothing you can do to establish in advance what the check in agent/Baggage services will decide on the day! If you speak to MEL baggage services, record the call and get the name of the person you speak to.