One thing that did not work between CO and NW: As I was checking in, but unfortunately after the agent had printed boarding passes, I asked the CO agent to remove my OP number. I did not automatically get the OP miles on the first leg, but got them upon writing to CO. When I wrote to NW about the second leg, NW refused to give me credit because the boarding pass had my OP number on it. I even gave NW my CO PIN so that they could check that I did not have CO credit. NW kept the boarding pass. I have not yet written to OP about getting OP credit on the NW leg. It was a NW ticket, so I do not think I can claim credit on the Internet.