Confused by Aeroseek and Flightstats
BA285 will be the commercial flight number.
BAW11M will be the air traffic callsign of a particular flight.
The online flightrackers take their info from ADS-B data which displays the callsign. They then use tables to equate a callsign to a commercial flight number. These tables can be innacurate as the data within is not supplied by the airlines.