Lets say that the best indicator of acuracy is the response of the recipient. Bob Fitzsimmons: if you think that he was a technical dinosaur, then you would have to fall back on his punching acuracy to explain the way he knocked heavyweights out so brutaly, because there would be no other possible reason left. Sam Langford: This guy would thread an uppercut through an opening in your guard barely bigger than his fist, and you wouldn't know untill you jumped up after the count and started fighting your cornermen. Jimmy Wilde: This guy might just have been the most dangerous fighter with a single punch, pound for pound. To be a Julian Jackson style imobiliser, in the flyweight division, you would need incredible acuracy.
Nobody probably thinks of him in a thread like this but at his short best Mike Tyson showed an unerring ability to catch good heavyweights clean and very early.