For what it's worth, our Chief Pilot in the 1970's told of his time in the RAF when he took part in Chipmunk spinning trials, in Australia I think, to try and find out why there was a tendancy for Chipmunks not to recover from spins.
He said that after months of testing they came to the conclusion that the problem was that as pilots followed the classic recovery drill, when moving the stick fully forward it met an aerodynamic lock that felt exactly as though it had reached full travel. The solution, he said, was to get a boot on it (ie the one not doing the "full opposite rudder" bit) and shove the stick forward another inch or two until it did hit full travel.
I'm no expert; that's what he said. I tried spinning one a few years later, admittedly from a very great height, and it recovered easily without using the spare boot. But perhaps the strakes were another part of the solution?