I don't really understand what you mean? I saw American 20.. But also the Alaska flight, and soem Qantas flight were due same time and all showed the same info but only the American 20 fight was shown.
Airlines may sell flights operated by other airlines: http://en.wikipedia.org/wiki/Code_share
It shows up under all flight numbers at the airport, but it is only one plane that flies and ATC only uses the flight number of the operating carrier
. (In Europe ATC flight numbers can be completely different from the numbers shown to the passengers.)