NW tickets will only show up on another airline website if there are flights operated by the other airline.

For example, my NW award flight coming up involves CO --> CO --> KL --> NW --> DL flights. The outbound flights show up on CO.com, NW.com and KL.com. My inbound flights show up on NW.com and DL.com.

They each have their own record indicator as well. I had to pull up my CO via the CO PNR, DL via the credit card (since I didn't have the DL one) and KL PNR was the same as the NW PNR.