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I recently booked 4 plane tickets for the same flight for myself and three friends. I have a Known Traveler Number for TSA Pre-Check, but none of my friends do. When we printed our boarding passes at the airport, all four of us had TSA Pre-Check printed on the boarding pass. The same was true of the return flight. Was this because I had a KTN? Did it matter that I was the one who booked the reservation (i.e. if one of my friends had booked it but still entered my KTN for my ticket, would we all have gotten Pre-Check)?