My first leg for the 100K marathon was a weekend trip YEG-YVR on Cdn, my primary one- world carrier. Since I am Gold on Cdn, I booked the res with that number. However, when I checked in at YVR, I asked the agent to credit my resurrected AA number for the return. She had already pressed the buttom, and my first boarding pass came out with the Cdn number on it.

However, she fiddled with the screen and replaced the Cdn+ number with the AA one, and printed off another boarding pass to see if the AA number "took". It did, and appeared on the new boarding pass. While I used the original pass to get on the flight (it was my eticket as well), I kept the small portion with the AA number on it. (and will file all my boarding pass receipts in an envelope for eventual mailing to the respective programs when one or more carriers screws up.)

In a few days, I'll check the online versions of my accounts to see which got credited where.

I booked flights on AA and CX, and will be doing the same with BA and IB later this week. On all these, I will use my higher status Cdn number outbound, then manually have the AA number put in on the return. (Unless the agent will record both at booking. Didn't try this with AA and CX since they can be dealt with reasonably if screw-ups occur. I'll try it with BA, see what they say. As for IB -- we've all read out them, eh? -- I think I might have them issue separate tickets on separate files, one each to Cdn+ and AA.

Will update you on my findings thus far soon. Thanks for starting this strand.