Before the investigation of this accident, I had never encountered the concept that control reversals might break an aircraft even at less than the manoeuvring speed, and had the mistaken impression that this theme was a relatively new concern.
I was browsing some NACA reports last night and came across
Consideration of dynamic loads on the vertical tail by the theory of flat yawing maneuvers.
It concludes that a sinusoidal deflection of the rudder reaches the design limit of the aircraft much more easily than step or impulsive deflections. It was written more than 55 years before AA587 lost its fin.