It's easy to forget how "new" this doctrine is. The foundations starting in the mid-1960s when Jeff Cooper and others, including Thell Reed, Eden Carl, Ray Chapman, and Jack Weaver began holding regular competitions in the San Bernardino Mountains of Southern California. They were experimenting with techniques to more effectively use the handgun for self defense. Those competitions begat IPSC.
And a consideration, in addition to shooting a reasonably powerful handgun fast and accurately, was being able to handle a lethal weapon efficiently and safely in a dynamic environment.
I went to the academy way back in the stone age of K Frame revolvers, dump pouches (uniform standard), and optional speedloaders (which I carried religiously). The holster we were given at the academy, along with the 4" Model 10 or Colt Police Positive was the old Bianchi 5BHL Thumb break, or a Jordan River Holster...old guys will remember these. Both had open trigger guards.
When I graduated and could buy my own leather, I immediately bought a Safariland SSIII retention holster with a covered trigger guard and mastered that holster. It was the model of holster I carried, not matter what the evolution of our duty guns were...the SSIII was the best.
When we were taught back then...the manual actually stressed
"taking a full shooting grip on the revolver, simultaneously gripping the handgun, releasing the snap, and placing your finger on the trigger as you begin your combat draw"...or wording VERY similar to that. Even back then it didn't make a lot of sense to me to engage the trigger
before I had at least got to a parallel muzzle orientation to the ground. Yes, there were a few premature BANGS on the range. Not from me, but you get the idea.
I had already been reading Ayoob, Cooper, and Jordan enthusiastically, as well as Askins, Nonte, and Skelton, but even back then the whole idea of
combative pistol shooting was in early, but rapid evolution.
Yes, Cooper at the old Leatherslap had begun the revolution and we are lucky today to have all of that information.
I am going to look for my old training book from the academy and see what other archaic info I can post up.