I also had CO Onepass reward tickets on NH. While transiting in Tokyo, by chance stopped by transit kiosk to request for a seat change. Agent could not find ticket number, but managed to call CO at Narita --- then had a supervisor step in. Fortunately, all worked out. However, if I just went directly to the gate with the CO issued boarding pass, I am sure I would have missed the flight while trying to sort out the ticketing.

Agree, always call the operating airline (code shares tickets, reward tickets, etc.) and get that airlines record locator number and e-ticket receipt if possible. Have flown on so many codeshares flights that I now prefer to be ticketed on the operating carrier's flight. One gets bounced around when trying to make changes (the code share carrier asks you to call the operating carrier and the operating carrier asks you to call the code share carrier...repeat).