Would AA allow me to book a JL-operated flight on AA code for the Japan-US segment? I remember reading somewhere on FT that flights should be on prime codes but I don't think this is a requirement in the oneworld explorer rules. Thanks.
There is no requirement in the rules for prime flights, but in my experience AA usually refuses to book flights as codeshares, except of course for AA codes. AA will be happy to book your JL (or any) flight as an AA code.