Using a NWA cert for a CO flight
 

I have a NW PD 727 which clearly states that Im entitled to $35 off any published fare of 200+ on NW, KLM or CO. When Ive called CO to book they tell me that I have to book it through NW, who then tells me that since the flight I want to book (EWR-DEN) is all on CO metal, I have to book through CO....UGH. Does anyone know how to work this out?

Book through CO, not NW. Give CO the reference code and exchange the certificate for your ticket at the airport, CTO, or ticket by mail.

You might also consider, you can use the discount certificate on NW's website if you can manage to get it to pull up the CO codeshare flights you wish to be on. Then everything can be done online.

NW can book 100% CO metal, but they can NOT book CO non-stops per their codeshare agreement.

EWR-DEN = NOT OK
BOS-EWR-DEN = OK
EWR-IAH-DEN = OK

Looks like this has to be done by CO if you want the non-stop.