While this is one reservation to you, it's really two reservations on one ticket. When you first booked the flight NW gave you their confirmation number and sent the info on over to CO. CO system is seperate so it makes it's own reservation record in its system. Once this is done other then changing flights, the information is not passed on again to CO. This is the same reason NW can't change a seat on a CO flight or vice-a-versa. The CO agent would have had to removed your account number and then reinserted it for the status to show up.

flyerCO