Well in a round-about way it is. When you give your ID, it's being checked against the data was was submitted by the airline to generate your boarding pass for a match. If you had included your KTN on your reservation, your boarding pass would have (most likely) had the precheck indicator, and for the same reason you would have been given the benefits of it when your ID was checked. The boarding pass is the only indicator to you before you get to TSA as to whether you qualify for precheck on the trip. (Some airports, even when TSA is not checking boarding passes have personel requiring you show the precheck Indicator on your BP before being allowed in the precheck line).