D0 has created a lot of pressure to get boarding groups moving and gate agents sometimes take liberties with the interpretation of boarding groups, perhaps because a flight is delayed, has a potential weather/crew timeout situation or if it has a light passenger load.

Flying AA F from LHR recently, F, J, and OneWorld elites (including Ruby) were all called at the same time, having the appearance of half of the plane boarding all at once with the normal coach boarding groups pushing right on their tails.