Originally Posted by
huge
Sounds like a plan ... I got an extra data point, forgot that Mrs Huge had taken a flight under similar circumstances with her Delta Platinum Amex - she was shot down in Seattle (where Delta and Alaska are feuding) but got away with it elsewhere.
Confirmed that it worked away from Seattle, at least for us. The ticket counter rep explained that we didn't get a free bag automatically because our Alaska FF numbers were entered, but said it wasn't a problem and took my Delta FF # to verify that my Delta Amex was registered, and then let us check one bag each for free.