From my understanding that is pretty much it,

I believe Cdda tries to emulate real world protection, so I like to believe vital protection protects you from vital damage like insta-kills and artierial bleeding which i guess is equavalent to critical hits. I, at least, recall more reliable combat outcomes if I made sure my "vitals" are covered for example brain and heart.

Damage protection generally has from the last time i played a low, median and high value which i guess emualates the idea of average hits hitting armour, hits on weaker parts of armour or "glancing blows"

So to my understanding when armour says something like 90 coverage on it, it means it covers 90% of a body part is covered and thus provides its values 90% of the time as there is still a 10% chance that you get hit in a part not covered.

The other values that use different materials like leather and kevlar with something like 80/20 means that 80% is one material and inherits its properties and the 20 % inherits the other to my understanding.

So good layering and part coverage makes the armour values

That is to my understanding and open to corrections