No, modern soft armor is definitely has a one-use aspect to it. As an undergrad student, I had a design project in a composites course. The topic selected by my design group: body armor.
We called up and e-mailed body armor manufacturers for input. One lesson: the panels of kevlar or other ballistic material were in pockets in the nylon carrier vest specifically because the ballistic material was mussed up when shot.
When hit by a bullet, the core layers of non-woven fabric are smushed (<--technical term), moved out of position, and generally have their mobility hindered. Since they disperse a bullet's energy by moving and tugging as much of their length as possible, the ability of a vest to soak a bullet goes down with each hit. (Which is why the core layers aren't woven - woven fibers are locked down by adjoining fibers and thus don't spread the energy as well. The outer layers are woven to act as "catcher's mitts" to the bullet, but don't perform the critical duty of spreading the impact.) The manufacturers I talked to recommended replacing a ballistic panel after it was shot even once.
Ceramic hard inserts are very often single-use. Except for really pathetic bullets they can stop with their ceramic uber-hardness, the ceramic panels absorb energy by cracking and shattering. The process of forming cracks needs energy from somewhere, and the only place to get it is the bullet. The ceramic panels also do the good deed of blunting the bullet, which makes the life of the inner fabric armor layers much easier.
Obviously, the vests can stop more than one bullet. But when you have a chance, get the vest's ballistic panels replaced.
Since most police make it through their careers without getting shot, and fewer are shot in more than one incident, this disposable armor approach seems acceptable. For dumb asses who get shot several times a month (runners), the expense of new ballistic panels might fall under cost of living expenses.
Anyway, I wholeheartedly recommend the armor degradation rules in...the SR Companion? Requiring a medium wound for armor degradation to occur seems like a very reasonable threshold between "armor damage not worth tracking" and "worth altering armor values."