There are two unique distinctions the airlines focus on, one is cancellations prior to day of departure, and the other is no show at the gate. Both are forecasted independently and incorporated into the overbooking profile for the flight. At the moment, most carriers use historically booking/cancellation statistics to forecast the cancellations prior to departure, and information from the departure control system to forecast day of departure no shows. I know the airlines have discussed drilling into lower levels of detail such as e-tickets over paper ones, if passengers order special meal options, connections, interline bookings, Frequent Flier profiles etc., to get better forecasts, but as far as I know, they either haven't gotten to that level of detail, or they thought it created too much noise in their forecasts.

I think another factor that has contributed to lower no show rates is corporate travel. Many frequent fliers have moved to private aircraft as the price and convenience has become more reasonable and the hassle of flying commercial has increased. Those type of travelers were notorious for having multiple back up options if their meeting ran late. Taking them out of the passenger pool reduces some of the irrational booking behavior.