Well, having gone through this type of thing MANY times, I've found only one way to clear an GUC in AMS. Before you go to the airport (generally before the flight gets handed over to KLM, but it has worked later), I call Delta and beg them to process the upgrade. Delta has to clear the upgrade for KLM and them provide you the GUC certificate number and the activation number. Armed with these two items, I then approach the KLM counter and ask them to re-issue the ticket. It's worked 4 times this year !
Now, as bad as this process seems, it's significantly better than anything you'll find at CDG on Air France … I've never been able to get a GUC cleared there.