I got the X for the first time a couple months ago after arriving at ATL from Guatemala City on DL. I was late arriving at the GUA airport and had to go find the back office for Delta because the checkin agents were no longer at the counter... I had already checked in online for the flight but you must have a printed BP at GUA so I needed them to print me one. The agent gave me my BP's and I made the flight but the GE kiosk at ATL did not ask the usual question of "did you arrive on flight xxx from xxx?". The customs agent asked me where I came in from and if I had anything to declare... I told him, and said nothing to declare..and I was on my way.. no questions asked when leaving the customs are either.