My friend and I, booked on the same locator, became WP silver after we completed our outbound flight. As soon as we became silver elite, we called NW reservation to update our elite status on our reservation. Two days before our departure, all of our NW segments were upgraded (we were on a 4 segments MR). However, our first segment, which is on CO still showed a n/a.
We checked in with CO. We noticed that there is no elite status on our boarding pass. We checked with our GA to find out what position we were on the upgrade list. She said the system showed no status for both of us. We showed her our upgraded boarding passes, and she called NW to verify and finally put us on the upgrade list. She manually wrote down silver on our boarding passes. Since the plane is quite empty, she decided to give us more room by blocking the middle seat for us. When she reassigned our seats and printed out our new boarding passes, the sliver elite status showed up on both of our boarding passes.
When boarding our second segment, the GA said that my BP did not show up. He asked me to step aside and have another GA assit me. Eventually, she reprinted all my boarding passes.
Today I checked my WP account, mine shows a R/R but my friend's shows R/L. We both paid L.

I am not sure whether CO did not receive the update of our new elite status or because we were on the same locator.

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