Ryan Parker, a noted Okinawan pressure point stylist, entered the NHB cage to show the effectiveness of PPS in real application. Unfortunately, he was somewhat less than effective.
I'm not sure there are real examples of people using them under pressure against competant, resistant opponents to make them part of a high-percentage defensive system. (and FWIW, many grappling tournaments allow pressure point manipulation -- since they don't consider it makes a difference at all).
WRT the one punch knockout, its happened, sometimes due to excellent timing (Silva vs. Newton), but just as often a lucky break (Shembri vs. Sakuraba or Henderson vs. Renzo). For me it goes back to being low-percentage, and risky if anything goes wrong. For me, WCK is not about low percentage techniques, its about robust, layered, systematized strategies that can cope with competant, resistant opponents and the errors that may occur during a stress situation.