I find all the discussion of body armor interesting.
Without going into possible scenarios that I envision for it’s use, I will offer a little about my own personal training in regards to such.
We are fairly confident in saying that bad people of all sorts (including those who are state sponsored) may wear armor during their activities. For this reason, a good portion of the training curriculum should include placing rounds on target to specifically stop threats so equipped. This means that specific areas such as the sides, low back, face, neck, groin/hips, legs, are all specific targeted areas in addition (of course) to the traditional center-mass engagement. Looking at a lot of the armor being offered for sale suggests that the protected coverage areas are not that big, and many areas are left open to projectile strikes that most certainly would take one out of the fight, at least long enough for you to gain a position of advantage and finish your work. This is born of the fact that it is impractical to provide enough coverage to protect all body areas; one couldn’t move about freely if so equipped.
In the past, many professionally hosted classes I attended focused on placing two rounds to the body, center mass. Also taught in nearly all was the “failure drill”, being that if the first two center mass hits didn’t stop the threat right away after an initial assessment, another round was to be placed to the head. Going forward, IMO, every engagement should be treated as a failure-to-stop, without hesitation. Assessment can occur well after the target is down and more rounds have been placed while they are down, or retreating. This is yet another reason why citizens need standard capacity ammunition load outs. Be they magazines, belts, or whatever, capacity limits damper the ability to deal with body armor wearing threats. So, train with the expectation that your adversary will be wearing armor.