I'm with ASA and I have jumpseated internationally with NW twice. The first one was coming back from AMS. It took the KLM ticket agents a good 45 mins of flipping through their manuals and calling people to get it sorted out, so it might not be a bad idea to list either in advance over the phone, or stop by the airport the day before.

The other time was on a 757 from BDL-AMS. Had absolutely zero problem there.