Tom,
The earliest 110s have horizontally marked blades and they only say "BUCK". The first 110 had a steel spacer with an integral spring bar for the lock. These knives had the one line BUCK mark horizontally stamped on the blade. Next, Buck etched the stamp. If you will look at a Levine's Guide (any edition), you can see pictures.
The earliest 110s were thinner and rather rough, actually. The knife won early acceptance, but, to be honest, it needed a lot of refinement to make it a good knife. By 1965 or 1966, the knife was a much better knife and Buck has continually "tweaked" it over the years. Many of us believe that the availability of BG-42 and ATS-34 blades on PCKS offer the most outstanding 110s ever made. On top of that, you can pick from a wide range of inlay materials, optional fingergrooves, nickel silver or brass, handle pins or no, etc.
I use my PCKS stag 110 with BG-42 for dressing rabbits and it is incredible. I can force the blade through the backbone and it still stays sharp, even after dressing several rabbits. The only thing I need to do to keep the knife shaving sharp is make a few light passes with my Lansky diamond stones (medium and fine) and the edge is right back to optimum, even after cleaning several bunnies.
The crazy thing about the 110 is that it somehow became a "loss leader" and sells all over the country at about one-half the price of several other lesser knives.