Martin really fiddled around with their models and features in that roughtly 1932-1940 time period. Two different fork Eb implementations and some with no fork Eb, multiple iterations of design on braces and key guards and engraving, adjustable thumb hook/nonadjustable thumb hook, C# adjuster/no C# adjuster, octave keys from ring to loop, solid nickel alloy keys, nickel plated keys (?? need confirm), brass lacquered keys, and I'm sure there are some others.
I wonder what was going on in the executive ranks and design department, what they were flailing about to achieve. When they issued the Committee 3 around 1945, did they throw up their hands in triumph and say "Finally! We've achieved what we were striving for!" or did they throw up their hands in exasperation and say "Enough already! We've designed the damn thing five times now, just go out and sell it!"
Because they never made a meaningful change to the #3 once it was issued.