Dwaine, I'm not trying to be a nay sayer, in fact, in my previous post I encouraged the new investagation and provided the data form my Simplex. However, I thought you should be aware of previous efforts and the possible pitfalls.
Specifically regarding the stock rotation issue, we can look at the my two unmarked samples which came from bicycles of known vintage. If the markings are date stamps, and we assume Simplex used them as early as 1969, why are they not on derailleurs as late as 1972 and 1977? Are my derailleurs actually earlier than 1969? Are they replacements? Did Simplex just forget to stamp them? Or did Simplex only stamp those that incorporated design changes, pending depletion of the old stock? It's all speculation until we get a lot more data.
By the way, a neighbor has an Elvish with one of the final versions of the Prestige (the one with the formed, sheet metal nameplate/cover). I cleaned it up and looked all for a date code, hoping to determining when this version was introduced. It had nothing either.