Dave- that's precisely the problem; no concrete records of serial numbers for dating purposes are readily available.
I took an active interest in Robert Malerne; "The master cobbler" a while back, as more and more brands I was unfamiliar with kept popping up on Ebay, and I wanted to understand their origin, and while I kept no records, if I had to hazzard a guess as to when the above clarinet was made, I would say between the late 1950s and early 1960s, based upon seller's reports and the logo used. It may, in fact date to the early 1950s, but no earlier, I suspect. Consider that the 7 ring Malerne Professional was, with little doubt, the best of his own branded creations. Consider, also, that among the dozen or so stencils he made, his own branded instrument was perhaps near the best, but not the best of his creations. How can this be, you may ask? It goes back to the old adage that: "The cobbler's children are always the worst shod." It's the same reason you find exposed wires in an electrician's home and leaky faucets in a plumber's, cracks in the walls of a plasterer's home, and sinking foundation piers in the home of the mason.
It can be safely assumed, as some of his stencils have a consistently higher pricetag than others, that either an undue, highly biased, and poorly formed and founded value has been placed on those that have been coveted, or in some instances, true consideration, regulated by a tangible measure of quality has been factored into collectors' desires for some over others. No brand name or lack, thereof, will ever fool a good objectively centered technician. The play test in experienced hands does not lie.
It's not unreasonable to assume that some firms who enlisted the talents of Mr. Malerne had much higher expectations for quality (and paid more, per instrument, for finish work) than others. I am a trade carpenter, and would NEVER dream of investing the time and trouble in my own home that I have in my wildly imaginative customers' homes.
I am insterested in Phil's desire to collect more data on this matter. It should not be that terribly difficult to do, as the information is abundant in cyberspace, and on "that other woodwind websight". It's simply a matter of time investment and fact checking, but for that precise reason, I'll not be throwing my hat in the ring at this time, as my time is in short supply.