TATL flights operated on NW metal have a two digit NW flight number, flights operated by KLM have a four digit NW flight number, actually an 8 plus the original KLM flight number, so for example EWR-AMS which is KL 658 is NW 8658.
Vice versa flights on KL metal have a three digit KLM flight number always starting with a 6 for the US and Canada...
KL 601 is AMS-LAX
KL 611 is AMS-ORD
KL 621 is AMS-ATL
For flight operated by Northwest, KL uses a four digit code and 60 before the actual NW flight number so the two first DTW bound flights are
KL 6039 ( NW 39 ) and KL 6067 ( NW 67 )