I guess my thought on the codeshare thing is the opposite (not that it matters of course). I don't know about oneworld, but on the AC departure screens I've seen the same AC-operated flight listed for multiple carriers. Just this weekend, there was a flight YYZ-PIT listed four times! AC, UA, SK, and LH I think (didn't write it down). On that basis you'd be able to get almost five carriers by flying between Toronto and Pittsburgh over and over!

Assuming oneworld is fairly aggressive in codesharing too, perhaps other oneworld partners have their code slapped on AA or CP transborder routes. Using those to get five carriers would defeat the purpose of this kind of promotion, wouldn't it?

Thanks!
andrew