Have an upcoming trip to PIT.

NW cannot book BWI-PIT. Why can CO, when the flight is code-shared on NW's metal anyway? My employer has a credit from NW for me on a previously cancelled ticket, which does us no good if we have to book on CO.

Will my NW elite bennies still work (upgrades, etc.) if I fly on a CO ticket (with my WP number on file) on NW metal?

Very frustrating - I want to give NW all the biz I can but they don't make it easy.