Actually, there is an angle-of-attack rate effect on stalling angle.
It's one of the reasons gust loads can be difficult to determine. Helicopter rotor designers are also familiar with the effect.
I encountered this early in my career. Thirty years ago when I was a wind tunnel test engineer, we were testing helicopter airfoil sections in a blowdown supersonic wind tunnel.
The speeds were subsonic, but we could use variable tunnel pressure to change Reynolds No.
The airfoil sections were held in 2-D insert and oscillated at various pitch rates.
I hadn't been taught about aerodynamic hysterisis (sp?) in school so it was quite interesting to see the effects of angle of attack rate (and Rey. No.) on stall angle.