I'm not sure exactly, but I believe when pilots and f/a's from other airlines non-rev on us they purchase a standby ticket from YYY-ZZZ. It is not a ticket for a particular flight, just particular city pairs. I also think it is not even date specific. Basically if a pilot or f/a uses us to commute to work (say a NW f/a living in NJ who commutes to DTW) and they have to go back and forth 3 times that month, they would purchase 6 standby tickets at the beginning of the month. 3 for EWR-DTW and 3 for DTW-EWR. Hope that makes sense.