My understanding is that now (as opposed to last year), you get AQDs on *A if the flight is part of an AC fare on an AC *014 ticket, even if not booked under the AC codeshare flight number.

That's what I did in February. AC booking engine wanted to put me in Y on their codeshare from HKG or NRT (I forget). B&M agent was able to issue same ticket with the same segment in J on the native flight number, for a mysterious $3 more, plus his ~$30 booking fee. Of course, could depend on the specifics of the fare rules, but when I've looked into it (which wasn't that time) even AC Z and P fares generally only prescribe that the transpac or transatlantic actually be on AC (or JV partners).

I got AQDs for the whole thing.

Good luck!