Since this term was blasted as not being valid and not to be found or heard of, I searched for the term on the web where I had first encountered it. Well last night when I was reading Steve Anchells "Darkroom Cookbook" I came across it again. PG. 79 half way down the page, where in big black letters it says NOTE you will find it in the next paragraph talking about old emulsions. Though this was in reference to paper, it also has been used in other publications (given time I will find them) that yes silver rich as a term, deals with old emulsion films too. Probably in the same book!