I have some devices removed from a drywall house.
I opened them up to see what I had.
The first thing I looked at was the cut off wires. When you slide the insulation off you find the wire under the insulation is shiny copper
I took the (Decora) snap switch apart and it looked pretty good inside. I suppose that is because a switch is fairly well sealed. The contacts were in excellent shape.
The problem showed up when I opened up the receptacle. I suppose it shouldn't be surprising but the contacts inside the holes were contaminated. I doubt the user would ever know because a few plug insertions would flake off the black stuff but the receptacle was affected.
I wonder how a T/R would have done?