Good observations, Barry. Since I was involved with Sterling starting around 1989, I can comment on some of the legacy stuff.
You're correct that the slide-end reinforcing rings were used for a while. Paul and I discussed these. I liked their looks, and Paul thought the horn looked cleaner without them (and was easier to make). So some Sterling had them in those days. As far as I know, the Virtuoso model never did.
I'm not sure exactly when Paul began to use Bauerfind valves (I believe he has switched to a different valve now). But in the early days, Paul's folks made the valves by hand. I watched a set being made on the workbench, and it was the first time I saw how complex the task was! Also, in those days the stainless steel valves used a round nylon valve guide instead of the rectangular shape that is almost universally used. I actually liked that idea!