I remember all the turmoil about the brake stay bolts, ans it IS important that they function properly. To that end I think the main reason some of those bolts have failed is improper installation. The bolts are "shouldered" with a smaller threaded section for the nut. The main function of the bolts is to act as a pin holding two parts together. The shoulder section fits through the mount on the swing arm AND the hole in the brake stay rod. The nut just keeps things in place, but the shouldered section of the bolts is what takes the load, that's why it is so big in diameter. It is all too easy if you don't look closely to get the bolt part way through , enough to start the nut on but the bolt not all the way seated in place. This would allow the threaded section to bear much of the load which that part is not intended to bear. And by tightening the nut the threaded section becomes over stressed and can bend/break. It is very important to visually check that the shouldered section goes all the way through both the end of the brake stay rod and the mounting bracket on the swing arm before the nut is tightened. The nut is designed tighten against the shoulder of the bolt NOT against the stay or swing arm.
For the connection to the backing plate the bolt goes through from the back side so the head of the bolt fits into a recess just the right size to keep it from turning, and the threaded portion AND the shoulder fit through the brake stay arm, then the washer and the nut go on. Again, the nut tightens against the shoulder NOT the backing plate. When everything is tight this system allows some free movement at both ends of the brake stay rod.
I know about this stuff because many years ago I broke a brake bolt like these when I started the nut on and wrenched the nut down tight only to spin the threaded section off with the nut. It wasn't through all the way, and because the bolt was not properly aligned for the intended force it got uneven stress and came apart. It isn't rocket science but it IS important to understand how it works.