The books I read by Applegate while in the Marine Corps didn't mention where he learned the techniques from (but the Marine Corps was never good at giving sources).
Memory says that Applegate was sent to Europe to train with the Commandos and their infiltrators (the ones that went in to work with the Resistance in Europe), can't remember what they called that group, and worked with Fairbairn then. Also, IIRC, Fairbairn was brought over for a while to work with the OSS instructor cadre when the OSS was being established.
Again working from memory, Cooper and the Bear Valley Gunslingers started running their research competitions in the mid-fifties. Sometime relatively soon after the Colonel had regained control of Gunsite, if I read and recall my reading of the Commentaries correctly, Cooper decided he had learned what he needed to learn about fighting with handguns and moved on to his original and primary love and passion, the study of the rifle.
If you want to see point shooting as it has been taken into the modern day and age, then Roger Phillips is the man for that.