Just booked the following, 2 pax all J, for mid next year and thought I'd share my experience.
MEL-LAX-JFK=EWR-(CTY)-YUL-(CMN)-LGW=LHR-CMB-MEL
As many are aware, due to Qantas' very limited
point of sale countries, flights departing from such locations (e.g. CMB, GRU) don't show up in award tools (you need to cross-reference availability from other carriers) and are only bookable as an additional leg. However, it seems flights departing CMN are not bookable even in this way. Flights that only stopover in CMN are also seemingly not bookable via the multicity tool despite being bookable individually. Because of this, I intended to book all legs except YUL-(CMN)-LGW using the multicity tool then cop the 5k point penalty to add that over the phone.
Now, I booked the above for 2 people, but as separate itineraries, because for the LAX-JFK leg, I couldn't find availability on the exact same flight in J, but did manage to find flights with departure times within an hour of each other. However, when I went to book the 2nd itinerary, I received the dreaded 15079-23951-420 error. I dropped a couple more legs from the itinerary and managed to get past the error but didn't yet pay. I then clicked 'Start Over' to try add some more legs but found that the reward seats for the legs I had added in that last attempt hadn't been released.
So off I went to make the booking over the phone and it was as painful as I expected. It took a while for me to get across that some of the reward seats that I was trying to book were still being held in a lost booking attempt and weren't actually unavailable. They got confused and assumed I was referring to my first, successful booking, but did eventually manage to recover my lost booking attempt.
This has been said many times before, but if you book over the phone, never use the term "Oneworld" at any point, say you want to book a business classic reward and just list out your legs. Also don't mention implicit stopovers as they will think you mean explicit, separate legs. The reward availability is obviously different when entered that way. Once they've searched the intended route you can then mention departure time and any expected stopovers if needed. I didn't make either of those mistakes by the way, but the operator still managed to do the wrong thing...
We got there in the end though and apparently there was phantom availability on the LHR-CMB leg and that's presumably why I was getting an error online. So we moved that flight to a different day and all was good. Amending my original successful booking was much simpler and the 5k point cost was worth the time saving.