You "forgot" to include those people killed by the murders who go free when someone innocent is hanged in their place. Which is very much an unknown unknown in this foursquare you tried to draw.
No one remembers the four people John Christie was able to kill precisely because an innocent man was hanged. They are very inconvenient, as they will never ever go away and allow the hang 'em high brigade a clear run at barbarism.
It is astonishing that in a month when the mistaken release of prisoners has been a feature, that some people still have enough faith in the justice system to allow it to kill people. They are either dim beyond belief, or very much the sort of people who pull the wings off flies.