You also have to go to the Pre-Departure Clearance centre prior to flying to the USA. This is where they ask the security questions that they used to ask at the gate when Schiphol had gate security checks. Takes a couple of minutes depending on how busy they are. IIRC there is a 'short-connection' lane available there if needed. Once you do that you get a receipt which also shows you your actual gate number. It at D1 for Delta (and I assume KLM as well) and E4 for other airlines.