This is how SkyTeam works ....
Flew last Sunday AMS-EWR on KL, and onwards to RDU on CO. No single KLM person in AMS could get me a seat assignment on the CO flight. The statement made was the well known "check with the transfer desk in EWR".
For "convenience reasons", you have to switch terminals in EWR (

) when connecting on CO, so I nearly missed by connection. After I already boarded on the CO flight, the gate agent came on board and pulled me off the flight as "the flight was not paid for". I insisted to be put back on the flight, and requested that she put some investigation into it. It turned out that, according to the gate agent, KLM had "downloaded" the booking information into the CO system for both the codeshare KL number as well as the CO number. .......

When complaining about the inconvenience (not to mention the fact that all the folks on board heard about the "not paid for" statement) and asking for the possibility of an upgrade, she said that no upgrades were available. She did not even apologized for the situation. There was still one seat left in First, but after the door closed, one of the crew members who was apparently off-duty took that seat. Thanks so much for your customer first policy. I would not be making many flights if I would adopt that same policy with my customers.