I wonder if there are many (or any) accounts of actually how combatants were captured during battle. I imagine that it would usually involve a lil bit of rasslin.
Given that the primary melee weapons of the era of full plate are fairly long two handed polearms afaik I'd expect that the majority of disabling blows (in pitched battle between infantry) come from thrusts into gaps/weak spots or from just smashing into the forearms or hands and breaking bones. But as pointed above, in duels and presumably small scale engagements that we'd see in TTRPGs fights between armoured opponents often devolve into grappling - and it's worth noting that the weapons themselves can be used as levers to grapple once you're in that range, which I don't know how you'd model in an RPG.
Of course the other point that's usually overlooked about plate armour is that it is a weapon in itself to some extent, if an unarmoured combatant attempted to grapple with a heavily armoured opponent they'd most likely be pummelled to death by gauntlets, kneecops or the elbow thingies. Hell, just imagine getting squarely headbutted in the face by someone wearing a heavy steel helmet.
Anyway, as to the actual topic of the topic idk but I think it's generally best to abstract the rules enough that this kinda thing doesn't really come up or it gets too crunchy. I think most combat systems should do away with initiative though (in terms of striking in melee combat) as that leads itself to a really dumbed down narrative (fights don't typically involve the combatants taking turns to swing at each other) and you'd get the opportunity to hit each other simultaneously, which as this topic alludes to is a pretty common thing irl.
For example of how that might work, if it's my turn to act and I attack you, instead of rolling to exceed your defence stat or AC or whatever, we could both roll attacks using the relevant skills/attributes of the system (with any modifiers that make sense here), with the chance for me to take damage if you beat me. I think this would work with a system such as the ASOIAF RPG, where you have "degrees of success", so if there was only a small difference between our rolls we could call that a parry and neither side takes damage, if we rolled the exact same number perhaps we both land a blow.
I feel like this would make combat much more dynamic as well as just making more sense, though it would perhaps start to get confusing when you want to add in modifiers, fight multiple opponents (I think that part could be easily resolved though) or want to use tactics - for example using a defensive stance might mean you subtract 2 from your attack roll but your opponent's degrees of success is reduced by 1 if they land a strike (degrees of success in ASOIAF are used to multiply damage for successful attacks btw).
And to bring my rambling back to the topic of the topic you could create some kind of rule for weapons that tend to have high stopping power, or for types of attack that do (slashing with a sword vs thrusting).
The ASOIAF RPG is pretty interesting from a realism perspective btw, I'll write more about it later if I remember but essentially it does some things very well but then it also throws in a ton of the classic RPG tropes that make it wildly unrealistic at times. It also needs a lot of rebalancing for certain aspects in general, particularly for power levelling (and combat should be an opposed roll reeee)
