From: Monk Alan Alan.Monk@tube.tfl.gov.uk
Yep; that sounds like my work! :-)
In 2008 I did a presentation at Naperville on "postwar shorties", as a primer for people to notice these older cars, and to explain how they could have a few running on their layouts. I've posted an abridged version of my car tallies to the files section of the group so everyone can see the raw numbers (I also posted the list from my 2009 clinic on postwar single sheathed cars).
Overall, the timeline is fascinating. In 1930, just before the Depression, fully 44% of the US and Canadian fleet were boxcars "less than 39'11" long". Once the Depression really took hold in 1931-1933 railroads purged their older equipment as fast as they could, and by 1945 the number of short boxcars was down to only 14% of the fleet (overally carrying capacity of the fleet was down too). In those 15 years over 410,000 boxcars were scrapped, with most being removed from service between 1930-1935.
By the end of the steam era (1959) only 2% (15,137 total) of the cars were shorties, and virtually all of those cars were either Dominion cars from the Great White North, or Ya'all Road ventilated cars. I don't have ANY ORERs from the 1960s, so I haven't tracked when the last cars of the type stopped rolling.
Oh; as an aside: when I originally crunched these numbers I was modeling 1950. Because of my results I recently backdated to the the late 1920s, simply because a 1950 car fleet can't support as many old, short, wood boxcars as I wanted!