Hello! I'm working on an Elgin, SN 16,158,497. Grade 354, Hunting. It's in a chrome, snap back & bezel cushion case. My question: when were chrome ww cases introduced in the USA? I have worked on quite a few 0, 3/0, and 6/0 USA watches over the years, and I suddenly realized that I do not know the relationships between when the movements were made, and when the cases were made...! As always: Thanks.