Years ago I was travelling on an industry stand-by ticket with Capitol Airways from JFK to SJU on a DC-10. Reservations showed it to be overbooked by some 40 plus seats. Even after all the stand-by pax were accepted there were still more than 70 vacant seats remaining on departure. Of course this was in the days when a booking could be made by phone without any advance payment. Overbooking had to be (and was) rampant.