Memory seems to be cemented when theres some type of value assigned to it, like a useful memory peg I find.

A major battle, a geomarker, usually there is SOMETHING noteworthy historical. I may not have put the labor into the volume of counties as you, but I've lived in so many places, and I index local histories of everywhere I live, and it cements so much.

Love the effort you put into testing your cognitive faculties!