I had come across that thanks to another poster pointing it further upthread. Where I got stuck was that the KLM screen is asking for some kinds of bizarre data, such as "valid for country" (OK, easy, it's the US - but *never* asked by any other airline) and "valid from" (what do I know? I know till when it's valid). All other airlines I have used KTN on only asked for the KTN itself, and not all the other data. It's simply not required by the TSA to recognize you as Trusted Traveler.