The way wait-lists worked you could sometimes "beat the system".
You got put on the waitlist. This was actually a queue (a list of bookings). The system would run through the queue at regular intervals trying to match waitlists against available seats. Suppose someone cancelled a seat just after the queue has been worked. It takes time, even if the queue is worked again immediately, to get through to a booking that wants that just cancelled seat. If you knew that and had your own robot working only your bookings you could sometimes beat the airline system to the seat. Indeed, it was quite possible for someone to grab that seat by pure luck and phoning at the right moment.