R100000-R190000 covers the years 1974 to 1977 so yours is probably 1975 or 1976. This data is from the "Standard Catalog of Smith & Wesson" by Supica and Nahas. Smith & Wesson could answer your query with more precision.
Great revolver and perhaps is actually the very best 5-shot Smith & Wesson .38 Special revolver ever made. Get rid of the scratches that you can and don't worry about the rest. Just carry it and shoot it and be happy.