IRL body armor degrades depending on what it is made of, how it protects, and how it is damaged. It can be complicated and it also depends on what it is made of and how it is used.
Military grade armor tends to be more durable since the soldier is going to be out in the field and under extended periods of combat - his armor will have to stand up to more non-combat wear and tear, too. The cop's vest will not have to keep out heavy rifles and not much wear on the materials is expected. So what about "adventurer grade"? What is its level of durability - that needs to be considered.
Body armor isn't like vehicle armor and it really can't be treated the same way. Vehicle armor will not only use the materials, but it will have layers of spacing, composite layers for different kinds of damage protections, and it is on a, well - tank or the like. It is designed completely differently and to be far, far more durable than body armor because it has to be since it is also a supporting structure for the vehicle in most cases.
Battle Dress might be somewhat analogous, but only a little bit.
Where vehicle armor only works by not getting penetrated, body armor works by (hopefully) not getting penetrated, and by reducing injury to the wearer if it does get penetrated by slowing the round and/or redirecting it. You might get a round through it but the wound won't penetrate deep enough to hit a vital organ. This slowing down can cause problems, too, since a high velocity round might now have enough energy to pass through you and then ricochet around a body panel (soft or hard) and back into another part of you, but then that is a reason why wearers have to be trained to use the armor right. You don't just strap it on and wade into combat expecting it work as advertised if you don't learn to wear it as a defensive tool.
Soft armor works because the weave used in the materials contracts and becomes rigid on impact. When I punch a soft panel in my vest I can feel the hardening effect depending on how hard I hit it and also see a clear impression of my knuckles and fingers in the material until it "relaxes". The fact that it depends on the layers of crisscrossed weave as much as the materials (which contribute to the resistance and durability), and that they react to impact is why soft vests not specifically made for it are not very effective for stab or cutting protection.
When soft armor panels are damaged by cuts or bullet penetration the armor is much less effective and the panels need to be replaced. Time also degrades performance, but less so than in the past.
Hard plates of ceramic chip and shatter to protect the wearer, absorbing and deflecting the impact like a fiberglass motorcycle helmet does. And like the helmet, the more damage done in a short amount of time, the more likely the damage will eventually get through to the wearer. Pretty much any impact that so much as hairline cracks ceramics will seriously degrade performance.
Metal plates are more durable, but the heaviest. Anything that damages one is probably heavy enough to ruin the plate, creases and dents included. But it depends, too, on how serious the ding is and what you expect to encounter. Mileage can vary. The additional risk is that metal plates can cause ricochets and there have been cases where that even hurts or kills a wearer when the round enters between plates and then bounces from one plate to another with the wearer's body in between.
So with all that in mind you need to consider what the damage is that might reduce the armor effectiveness and if the wearer will survive the experience. If you are using the CT system then it is all-or-nothing when determining hits so its hard to tell if a hit lands or shot misses. IN MT/Striker?AHL it is simple to tell if the target is actually hit or not - penetration is done separately.
I would argue that nearly any armor that is penetrated will need servicing at a minimum for it to be of any use at all in the future. And as a referee I would say in the case of anything but Combat or Battle Dress you'll be looking at a higher cost for repairs than just buying a new suit of Cloth.
Ablat, given its nature and how it protects degrades per the rules but the rules don't say how much.
For either of the above any actual HIT that doesn't penetrate will still require servicing. Maybe the reduction should be TWO points lowered from DM for penetration hits and ONE point for non? Just keep it simple and migraine free by not adding up all the hits - just say that in any combat period if the armor is hit the DM is lowered by one point, and then drop two more if there were any penetrations. Regardless of number.
For Jack, Mesh...same thing, but maybe less in some ways. The stuff is pretty much worthless for guns and less materials finicky so maybe just leaving it as is works? Or maybe telling the player his leather jacket is now ribbons would be enough?
For Combat and BD the armor will be more durable and (as I imagine) more modular in construction. Like heavy armor is today it will probably have components designed for easy swap-out when they are damaged to the point of uselessness and in the military this would be the practice if the armor is breached or heavily damaged. Units will have armorers for this. You could even argue that the higher the TL the less this would even have to be done?
To reflect that it is armor designed for far more than just keeping your local cop alive in a handgun fight maybe only penetrating hits would need serious work, and anything less would be just routine maintenance covered by having the skill to wear it - not just Vacc Suit. And really, anything that damages this armor will likely be serious firepower so it should be easy to explain that to the player who just got hosed with a burst of RAM grenade fire or survived a hit from a PGMP. There probably wouldn't be much left of the armor's integrity - but it will have done its job.
