I wonder if the delay in stall onset is based purely on wind tunnel data; I suspect so. In which case one question would be:
is the stall angle in a tunnel with sound effects higher or lower than that for the same aerofoil at full scale?
I'm wondering if it's a Reynolds number dependent phenomenom. (Im never sure how to stop spelling that word!). In which case it could be akin to transition strips, which help on a tunnel model sometimes but don't get the chance to be effective at full scale.