Funny thing is, even when damaged it would still hold back a standard F1 frag grenade while directly atop the blast. Mean while in life sucks world, the wearer would be turned into meat confetti BUT the vest is still good! XD
That was from real life tests. So I think the vest being damaged should still flatly stop a scaled amount of ballistic damage. If assuming you got shot in the chest.
New= frag / 7.62x51
light damage = some damage from frag but mostly in the clear / 5.56x45
damaged to falling apart = possible absorb 9mm and outer reach shrapnel but still gets hurt because of the gaps.
Caveat= There really does exist a chemical-esque treatment of small particles(that resemble milk) that can be poured onto fabric to make it stab resistant. In game terms, it could be implemented to treat clothing and armor to the affect of cutting/slashing damage turns into bash damage. So it would absorb the stab/slash/bullet/shrapnel, nut as a result it would be more prone to break your bones…which would be a toss up to the individual if that helps or hinders.
Could someone look this sh!t up please? Make a new thread and I’ll endorse it 
edit-
One small side note. Why don’t we have Titanium? Hard as funk to work with but, it is literally feather light and strong as steel.