Hello, I plan on travelling SYD > SPU (split Croatia) and would love to have it all on the same QF ticket (even if it's not a code share). I can do SYD > ZAG as code share which puts me SYD > LHR > ZAG. Or SYD > PER > FCO > ZAG with FCO > ZAG not a codeshare but booked with a Croatia Airlines flight number. Is there a way to have either of these routes but continue on ZAG > SPU with a Croatia Airlines flight number but have it all on the same ticket booked by Qantas?
In theory yes the main concern would be routing ofcourse. To give you a simple example, you can fly SYD to LHR with BA or QF, and BA even operates a non-stop service from LHR to SPU. The problem is the SPU flight is poorly timed such that if you were to take the QF flight there, you would arrive with a very tight connection (likely less than MCT) meaning it's unticketable. If you fly BA to LHR and connect to SPU that is fine and perfectly ticketable. In terms of other partners who fly to SPU, that's also a challenge. For instance neither QR nor EK fly nonstop to SPU.
What you may want to try doing as a first step is to give Qantas reservations a call and see what they can price out. They have access to more sophisticated booking tools than you or I have. Additionally, a skilled travel agent will likely be able to help you sort that one out.
I should add I have tried this with the multi-city tool but it errors out whenever I add SPU.
I believe for multi-city tickets QF is not allowed to sell flights originating outside of Australia and/or going to a destination other than Australia which is likely why you are seeing that error out despite BA obviously having a single nonstop option ex LHR
Additional question, is there any benefit having a QF flight number on a BA flight? I did notice these codeshare flights were slightly cheaper than the BA flight number of the same flight.
The main benefits of a flight carrying a QF flight number is several fold. First, you will earn status credits at the Qantas earn rate as opposed to the BA earn rate (which tends to be poorer). Second, for things like loyalty bonus and the 4 flight segment requirement to qualify for QF elite that BA flight carrying a QF flight number will count as a QF flight whereas carrying a BA flight number it won't. You would also have access to the EK lounge but I suspect that is a moot point given your status.
There are some benefits of carrying a BA flight number for a BA operated flight. For instance, I hear upgrades are easier to come by. Second, since you are now flying a UK airline by flight number you are covered by UK261 on the outbound and EU261 inbound trip. With a Qantas flight number you would only be covered on the inbound.
In terms of what to book it's really what you are after. Are you in desperate need of status credits? If so then choosing a QF option makes the most sense. On the other hand if you want a convenient itinerary and don't care if you leave a few status credits on the table booking something more direct like BA might make sense.