For another example of how many no-shows a flight can see, I recently got onto an American flight, flying standby, which was full in First, overbooked 4 in Business, and overbooked 10 in Coach. The flight, a 190 seat 767-300, also had 10 revenue standby passengers. So, with 24 more revenue passengers booked than seats available (about 12% over), they were able to accomodate I think 4 non-revs, hence 28 no-shows on one flight. The flight was CDG-JFK, the afternoon of the birdstrike. A lot of passengers headed to MIA on the flight that hit the birds were reaccomodated on this JFK trip.
American Way had a great Vantage Point article on this topic, don't remember whether it was from Carty or Crandall, but it doesn't seem to be available online anymore.