This blade discussion is really interesting.
As I was looking at Richard's photos, I had a thought. With anything but a flat blade, how much does the blade distort when spinning. If you look at an airplane prop, as the pitch is increased, the blade distorts and it is designed to do so. Do you suppose that with mower blades with the "wing" they design in a little bend so that when spinning at speed they pull themselves straight? Even if that were the case, I would expect the bend to be the same for each side of the blade, which clearly isn't the case in Richard's pictures.
Richard, I am not poking or stirring here. But I am now curious about whether blade designers design a distortion factor into the profile or not.