You’ve raised several interesting points of departure, coinnuttius, but I’d better just stick with my original focus—that the Standing Liberty quarters of 1917-1924 should have a different KM catalog number from those of 1925-1930.
When I posted the two pictures of the 1920 and the 1930 side-by-side I remember laughing to myself and shrugging my shoulders, wishing I had pictures on hand of two more thoroughly circulated coins—there just wasn’t enough contrast to make my case. So it didn’t really surprise me when you replied: “The Type 2a vs Type 2b St. Libs differences are not a large noticable change, nor does it cross date boundaries where it would be the "diagnostic" difference.”\
But I continue to think the “date atop pedestal/recessed date” is a very substantial difference—if not in 2-dimensional photos, then certainly in 3-dimensional metal. It was enough of a difference, anyway, that it definitely affected the way the two types circulated—or didn’t circulate.
In point of fact, the “date atop pedestal/recessed date” difference
is often diagnostic—as the coin pictured below illustrates. This badly worn, dateless SLQ is instantly recognizable as a “date atop pedestal” coin belonging to the 1917-1924 time period.
When I began collecting in 1964 it was not too uncommon to see SLQ’s in circulation—but
only dateless ones. (I picked the coin below off Pop’s dresser in ’65. It was an “S” mint!) But I never—ever—saw a SLQ circulating whose date I could read—or even try to puzzle out its remnants (as I did many times with the Buffalo nickels then still circulating).
And the reason the only SLQ’s that I saw circulating had their dates completely erased? Because I was seeing only the “date atop pedestal” coins of 1916-1924 (dateless SLQ’s of the 1916-1917 types 1a and 1b also still circulated). The “recessed date” coins of 1925-1930 had already been pulled from circulation by ’64 and were already sitting in the collections and accumulations that were (it seemed) in every family in those days.
Funny, isn’t it? The newer SLQ’s of 1925-1930 departed circulation before the older ones of 1916-1924.
Anyway, as I see it, the KM should assign the SLQ series 4 different catalog numbers, all based on obvious design differences along the following lines: 1a 1916, 1b 1917, 2a 1917-1924, 2b 1925-1930.
Finally, the San Francisco-mint coin below. It was at least 41 years old the first time I saw it—and it tortured me as a kid. That was 55 years ago, and when I look at it now I still wonder…1917s, 1918s, 1918/17s, 1919s, 1920s, 1923s or 1924s?

v.