Airfoilmod,
Have some funny notions in that place of yours.
There is no airflow assymetry in a crab, you're just setting the drift for the track you fly. Your airflows are symetrical on your wings. Otherwise, control would be needed.
Ball and needle would be centered in a crab. but for a ground observer, you'd be flying sideways.
Like John, for me, any form of assymetry is a slip although if you asked me, I would qualify a skid or a slip by the ball position.