So making a reservation with QF costs $25 in addition to trhe cost of the ticket? Maybe I'm being dense, but I don't get this at all. Please clarify where in this process I would get charged by QF:

Scenario A
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1) I buy a full fare round trip ticket HKG-SYD. The first sector I reserve and take on CX; the return segment of the e-ticket (as issued by CX) is open-dated.

2) I call QF reservations and make a reservation for my desired return QF flight, quoting the ticket number to them.

3) I arrive for my reserved flight and check-in at SYD.

Scenario B
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1) I buy a full-fare RT ticket HKG-SYD-HKG from CX with reservations initially on a specific CX flight HKG-SYD and on a specific QF flight SYD-HKG, both of which feature on the e-ticket. I take the initial flight as ticketed.

2) While in SYD my plans change. I call QF reservations and move the date of my return flight to a new one (still on QF)

3) I check-in at SYD for the amended flight.

Scenario C
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As per Scenario B except that it is a paper ticket (let's assume issued in some outport that can't do e-ticketing).