The pitting on the ring bottom face is due to this being the hottest area in the engine - where all the heat from the crown is tranferrred from the piston into the bore via the ring.
Thus formation of the free radicals always starts at this hard connection between the two faces.
A " normal " ring bottom face is bright and shinny, due to it being pushed back and forth into the Exhaust port.
Any pitting on this face is whats called " power deto " and is the outer limit, just before the piston starts being attacked and the EGT begins dropping.
Before I came up with the connection between deto and EGT drop, a few clever tuners learned to look for this ring pitting, as an indication they were on the limit.
Ripping the cylinder off continually is a pain, simply reading the EGT data logging is super easy and always reliable.