Ah, an important qualification!

Frankly I've never seen a sufficiently accurate and fitted harness put out of action by the accumulation of dents. Rent straps & buckles, lacing points sheared off, rivets blown out of articulations, et cetera; never a piece so damaged as to seize up entirely. However, I personally tend to avoid tournaments set up with that goal in mind. I participated in a farcical tournament at Combat Con last year where a lot of harness was badly dented. My vambraces looked like half chewed caramels by the end of it. The organizer was a fan of Elizabethan style tournaments where no thrusts and few close quarters techniques were allowed. So what's left? Bashing with the blunted edge. Really a complete waste of time, as far as I am concerned but no one had to bow out because a piece of kit was stove in. Armour works but isn't indestructible. Dents are a normal occurrence in full contact harness fighting.

I don't know if that answers your question but thanks for clarifying your intent in asking it. :)

Never had my harness dented so that it would somehow impair my movement or cause a serious injury. However last month I participated in a mass fight with blunt steel weapons where I had my backplate and helmet dented pretty badly by halberds (these were full-force blows by the way). No injuries at all, not even a bruise or a headache, but I would have quit due to safety considerations when I felt a dented backplate pushing into my shoulder. I didn't have to because by the time I felt it the last fight was over. The only injure I got on that event was a big bruise (though it wasn't painful at all) on the inner side of my thigh where there was no armor.

I occasionally have small bruises on armored parts of my body, mostly on arms, because I use relatively little padding under my armor and some parts are not fitted perfectly well. Probably the easiest way to injure a person with a cut to armor is to cut at his fingers (if he has fingered gauntlets). Vambraces can also be relatively good targets, depends on how thick they are and how well they are fitted. For some reason I never receive strong blows to the elbows so can't say if these are vulnerable or not. Legs are very difficult to injure, though on most authentic armors leg armor is relatively thin compared to modern reenactment armors.

I missed this topic before. I have a few comments.

I'm surprised a bit about some of the true/false and long/short edge comments. My experience is that almost everybody uses the Italian terminology indiscriminately, even if they are training in German longsword. It's not a big deal to me which people use, but I make a personal effort to stick with long/short foe Leichtenauer. Several published translations even translate langen/kurtzen as "true/false."

As far as bashing joints to immobilize armour, German Harnischfechten includes techniques for striking the joints (and head, of course) with the pommel. It may be supposition on my part, but I believe that there is an implication that in addition to damaging the actual elbow or knee, the goal is damage the armour joint. I'll try to remember to look for specific textual support.

I would never bother trying to damage armour with a regular sword stroke. I've had teenagers swing a blunt sword like a baseball bat at my torso wearing coat of plates with no significant effect. My old breastplate took a minor crease or two from the most abusive swings like this, but nothing that did more than make it look rugged. I know that joint armour is not the same, but I also know in a real fight my opponent won't be standing there saying "Yes, like that, but swing harder." Which is what I was doing at the time.