<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Damian:
I've not checked yet If CO has codeshare on AMS-WAW with KLM but I hope it does.
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Just to clarify the NW/KLM thing: you can get CO OnePass credit on NW codeshare flights operated by KLM. This should work in your case, since as long as the flights originate in the US (I think), e.g. USA city-AMS on NW, then AMS-WAW on KLM -- you usually get NW flight numbers all the way. And BTW, welcome to OnePass!