The rules for AA codeshares may vary by country. Ask the AA RTW desk. They would be keen on AA codeshares, as would maximize the AA share of the ticket.
If crediting to AAdvantage AA codeshares may not be the best for AA earnings. Need to do calculations .
Link--> https://www.flyertalk.com/forum/amer...age-miles.html

QF has some AA codeshares in Australia and trans Tasman (AU<--NZ). Guess will be for flights that could connect to AA long haul services.
Nothing in NZ as QF or any oneworld airlines do not operate in NZ. QF has some codeshares with Jetstar JQ NZ (LCC owned by QF), which are OK for *ONE* and GLOB* tickets

I'm not a ticket expert but what seemed to work for me was checking if the route was bookable on the desired codeshare airline's website. So for example if you want to fly from A to B with an AA flight number then see if you can book the desired flight on the AA website with AA codeshare flight numbers. If not you most likely can't book it because if the marketing airline doesn't let you book it then who will?

In my limited experience, AA RTW desk will be completely fine with assigning AA flight numbers but only if the other airline allows it. I don't know the logic behind what works and what doesn't, but AA has said that travel agents can book AA codeshares when AA themselves cannot. They also said that they can get the AA codeshare on routes that "touch" the US.. but everything else -- YMMV. Never hurts to ask if having the AA flt number is important (which it is, for AY earners).

Thanks all, this is for a planned RTW ticket with points credited to AY+. I was originally planning on using AY flights but having it ticketed by another airline, not realising that AY come up with a notional value so they can use revenue based points. I'm not so bothered for the "shorter" flights but keen to get 250% for the longer ones.

An important point to remember. Similarly, if you're crediting to QRPC, AA codeshares on QR metal give you better earnings than QR marketed flights on QR metal.

Codeshare flights can have traffic restrictions attached to them. Unfortunately I can't look up your specific example because I only have access to ExpertFlyer (not a GDS) and EF doesn't appear to be able to show traffic restriction codes for AA-marketed flights, but it's not uncommon for codeshares to be coded Q ("INTL ONLINE CONNECTING OR STOPOVR TRAFFIC ONLY"). For example, here's AY5096 (operated by CX134):

As I understand it, Q means that both stopovers and transits are allowed but only if it's preceded or followed by an international flight marketed by the same airline.

Even then, your mileage may vary depending on the travel agent you're using (including the AA RTW desk) as they've definitely been happy to book me on Q-coded codeshares even though the "online" aspect wasn't true. Conversely, I've had the rates desk change some unrestricted codeshares to the prime code for seemingly no reason. 🤷🏼‍♂️ (No those were not AA-operated flights)

The flight being available standalone is a sufficient but not a necessary condition. For example AA have been happy to book me on AA, AY, and JL codeshares (sometimes even despite traffic restrictions) even though none of those flights would be bookable on aa.com.

I am trying to ticket the following through BA:
1. KHI-DOH BA (operated by QR): transit
2. DOH-LHR BA (operated by QR): transit (as less than 24 hours in London)
3. LHR-DXB BA: stopover
4. DXB-DOH QR: transit
5. DOH-MIA AA (operated by QR): transit
6. MIA-JFK AA: stopover
7. JFK-DFW AA: transit
8. DFW-ANC AA: transit
9. ANC-DFW AA: transit
10. DFW-MIA AA: stopover
11. MIA-LAX AA: transit
12. LAX-HKG CX: stopover (AA not available in D)
13. HKG-DPS CX: stopover
14. DPS-HKG CX: transit
15. HKG-CMB CX: transit
16. CMB-KHI UL

The quote provided is 6253GBP, out of which 3449GBP is the base fare. This is correct. YQ is around 914GBP and YR is around 698GBP. RGGA (whatever that is) is 922.90GBP.Fare - £3,449.00

YQAD - £531.30

YRVB - £606.00

YQAC - £382.90

YRVA - £92.00

UBAS - £31.15

RGGA - £922.90

SPEB - £7.90

YDDE - £7.40

G4AF - £24.20

PZAV - £2.20

QAAP - £24.20

R9SE - £4.00

AEAD - £15.00

F6TO - £9.00

TPSE - £1.00

ZRAP - £2.00

AYSE - £8.20

USAP - £25.80

USAS - £17.20

XACO - £2.80

XYCR - £5.20

YCAE - £5.40

G3RE - £32.10

HKAE - £18.90

I5SE - £12.20

D5CB - £10.50
XF - £3.30

This feels quite heavy on YQ/YQ/taxes. I also have no idea what RGGA is. Any suggestions what I could do to reduce these? I know I'm going through LHR but have already limited this to a transit. I'm crediting to AY.

Flying out of the UK usually attracts a premium so trying an alternative to that might be a start.

I believe RGGA is the Pakistan Federal Excise Duty which applies to flights leaving Pakistan.
In this case, it's a flat 350,000 PKR which is roughly the 922 GBP.
This would apply regardless of what you do for a biz RTW ticket ex-Pakistan.

Not that simple.
Departures from most, but not all, UK airports has the UK APD -- https://en.wikipedia.org/wiki/Air_Passenger_Duty
For UK transits (<24hrs) APD is not charged.

Yes, indeed - this is why I have limited the transit in London to less than 24 hours.

If RGGA is Pakistan Federal Excise Duty as per @izzik then I wonder whether I should just start in Japan to ditch this and a ton of YQ/YR?

Doh !! I even knew that! Serves me right for not reading the itinerary properly.

Japan is regularly cited as one of the cheaper places to start a RTW ticket so might be worth a look if it's an option for you.