As mentioned above, you can't tell if it's overbooked just from GDS availability. A friend and I had a recent AS flight show F0 Y1 before disappearing, but when we asked a friend with access to AS load factors, he said it was booked exactly to capacity with no overbooking. (AS per their official policy will tell you if the flight is overbooked if you call them, but it was easier to email the friend. ) The amount of overbooking authorized varies by route, time, and and (of course) airline.