Originally Posted by HobokenFlyer
Yes that may be true, but those restrictions do exist. I don't think you can book a CO codeshare on a NW flight between EWR-DTW unless you are connecting to a NW flight or something like that....
So it's a combo; CO restricting codeshare booking and that some routing are invalid because of restrictions setup by the FTC/FCC to get the codeshare approved.
- HF
With a few exceptions, CO/NW/DL codeshares are not bookable non-stop.
However an overwhelming number of logical NW options are not presented due to the co.com bias programmed in by CO. You will have an extremely difficult time finding something as efficient and straightforward as DCA-MSP-LAX at co.com.
NW has similar logic at nwa.com programmed against CO.
It's only the third party sites who don't care what you book. They're your best resource for researching codeshares.