back to my comment above, up until the 'convertibles' there was NO reason to "have to, need to" UNLESS it was for a service, refinish or other some such event needing to "keep the parts" together for any particular gun...all the fitting was normally done at the "fitting " bench, pick up parts from a bin, fit them, and build a gun. test fire and ship it out...IF there was any issue problems, or need to go back through the system and to "keep the parts together" they would be marked, possibly, may not..................
unless even owner of every bearcat out there called in and reported their particular guns, much like Chad has been doing and trying to do, you'd be able to come up with a dividing line, base line......remember the vast majority of Ruger owners are NOT collectors, do NOT belong to any collecting group, either the RCA or ROCS, let alone subscribe to Chads RENE to even be concerned or care about the "scratches" ( numbers on the end of their cylinders, heck we see them ALL the time at any given gun show, and the cylinder in the gun does NOT "match" that gun, especially in the case of convertibles, they ONLY care that is feeds,fires and functions.......
I've looked at THOUSANDS over the years , guns shows as well as owning ,working at 3 different gun shops that "serviced" firearms, and I could not even tell you ,except in the case of an "obvious refinished" gun ( they usually are marked) and if the gun was a 'convertible" in the first place.................today the "new"??? Ruger company, and its various models in the course of assembly /fitting mark them , same went for the grip frames for a while, expecially for the Vaqueros,??? why ??? my guess would be as the frame was steel , and possibly had to be polished together as a unit, ?? other wise, as the aluminum frames were already made and finished to size, it would be a waste of time, effort and time to any production unit is 'money' 8)
Good luck and a nice try to possibly come up with a time frame , but many of us would be wondering as to "parts" or production changes, and some ,like S&W add a "dash" for any important production change within a model, ala model 10-5, etc. :wink:
one caveat is, if I, over the years have numbered , both with hand stamps, as well as electric pencil untold number of cylinders ,in any and all calibers and I was just ONE gunsmith , among untold, countless smiths, as well as kitchen table gun plumbers, which ones are factory and which one is MINE,,, or someone elses, yikes scary thought and throws a monkey wrench into ANY legitimate data table :roll: