On Thursday I walked past a gate at BWI and noticed that the Group B boarding sign was still blinking on the monitors - but there was no one left at the gate. So I would imagine that the flight had a lot of empty seats on it (the theoretical max for Groups A and B together is 120, but there are always empties in A1-A15, and the B group may not have been full either). I didn't notice where the flight was heading, but I'm willing to bet it wasn't MCO.