> NASA Video
E.Z Flyer, possibly you did not watch the right video or did not watch it all the way through. It starts off using a controlled environment and explanations, shows the profiles of observed ice accumulation, and how they were recreated to disrupt air flow, and how the air flow on a tail assembly breaks loose, how the reconnection point steadily moves toward the rear, and how that reconnection point eventually reconnects on a movable rather than a fixed surface, deflecting it.
It does take patience to watch the video through the educational material.
If you quit partway you will have missed the actual videos taken in actual flight by the actual test pilots, including the actual tail stall experienced while they were trying to creep up on the conditions where it was expected.