The idea in Pure Krav Maga was to optimize the curriculum as the concentration of the essence of H2H, and optimize the learning and drilling methods to learn the material and on top priority to create a set of virtual techniques that will suit any attacker and any defender against any non virtual form of attack.
Often in Fairbairn Manuals and historical videos present collective evidence and clues to what the Fairbairn H2H training method essence was about. I would not expect they to be an accurate copy of the whole system since it is simply too hard to account for the chain of evidence in history.
However few key principles and comments from observation and analysis I can make:
In grappling, you would find a demo of a sort of reversal of fortunes in grappling scenarios by preemptive use or retroactive use of a pressure point in the human body. With no qualms over what the historical evidence about the Fairbairn training methods, I would like to see in a demo how it works when an opponent is approaching with intent skillfully quickly and attempting to cause harm in one way or another and how one technique or other is useful in stopping it. However this excellent approach of poking pressure points on the human body seems to be under emphasized in drilling due to fear for safety concerns.
This is what the human nature of kids, civilian and soldiers had always debated on. The fluid act, play and realistic training against fluid execution of deadly threats. Often, training was diverted to safe grappling and safe method of exchanging blows and kicks amounted to off reality fitness and endurance improvement.
In the long range, there are few preemptive direct attack drilling as well with basic direct front kicks. You cannot tell however that they had the most efficient lunging efforts but rather kicking from the spot on time would work... It is necessary for a good complete self defense system to utilize the precious time and finish the job as early as possible, therefore additional training to reversal of fortunes form a greater distance is possible and needed to be drilled. This is what Pure Krav Maga has done!
As for Fairbairn Pistol threat defensive techniques from the front and back while defender's arms are assumed to be in a surrendering "hands-up" position an almost Hollywood characterized refinement of instinctive protection positioning of the arms over the head which of course is a waste of time and would be no use against a bullet.
Then we have pistol threat defense from the front. In Pure Krav Maga this approach was adopted originally by Imrich but from initial palms positioning at the waist and not palms up. Efficiency and maintaining the element of surprise, finishing the opponent as soon as possible, not letting time lapse in an unfavorable risky positioning is the key in Pure Krav Maga.
The most important trust students could gain in executing this technique is not only understanding the concept of reaction time, but testing it realistically with let's say the intent and the training of the attacker role to squeeze the trigger promptly upon various virtual scenarios that encompass any option that is workable.
Realistically to train someone to move his two hundred pounds body and get a 36 inch average waist away from a barrel pointed to the center requires much more thought. The spinning should be triple the speed presented in this video, and is achievable by a set of commands and focal point one must assume to execute this spin!
As for Fairbairn Military Knife training it amounted to use of a dagger for sentry removal from any available angle reach for a finishing lethal stab and few blocks of stabbing. It did not however have a complete unarmed methodology of training against knife. In addition Pure Krav Maga was the first to have the most complete realistically workable defense against the straight stab. It also categorized levels of efficiency in attack and therefore ensured virtual techniques are created against most efficiently severe virtual forms of attacks.
Finally as you can see the military although not training in the average form of a martial art, did assume the kata form of drilling motor skills to be versed in the technique before trying it on a live training partner.
While Fairbairn is known to steer from the traditional years of Jujitsu and Kung Fu training into a quick grasping of principles of prevailing in unarmed confrontation based on simple logic, yet its training system while providing an excellent initial approach into thinking and covering intensive unarmed combat training, could have used the complete circuit on all the virtual levels of forms of attack, complete theory and application of unarmed combat training system that Pure Krav Maga has!