My guess is that they are minor leaks and that some of the encrustations are from minerals in the water. On a former HWT I had replaced, the TPR had a very small leak and it completely filled up the discharge port with minerals to the point it couldn't be manually opened. I would expect a TPR to not have dissimilar metals causing electrolytic corrosion but then maybe they were not designed to have moisture constantly present on that part of the TPR.
Probably there is some dissimilar metals at play and possibly there is a small leak that provides the water to set off the electrolytic corrosion. The ball valve probably has an impurity in the metal and a resultant pinhole. I suspect the leak will increase over time but don't expect a catastrophic failure.
The tank is likely leaking a little at the threads. I would unscrew it, clean up the threads, and reassemble it with Teflon tape.