Usually, but not always. I had a LHR-SYD flight last December on BA. My AA number was listed on the boarding pass, but the points ended up in my QF account. The QF number had been in the system because I had flown Transatlantic on BA on the same trip (not eligible for AA points).

I didn't bother getting the points swapped over. The AA status qualifying year was about to end and I was nowhere near qualifying for the next tier.

So it was very odd, but apparently the boarding pass does not always have the last word.

Alan.