There appear to be two different guns shown in the photos on the scanned page in Post #7, and neither are a standard Model of 1921, nor a Model of 1919 variant. The gun in the main photo being shot by Hedges appears to have a barrel longer than the 10.5" one normally seen on the Model 1921, but it is not of a heavy profile like that of the Model 1923. Speaking of the Model 1923, the gun has a Model 1923 buttstock equipped, which has much less drop and is fitted with an M1903 butt sling swivel. Another sling swivel is fitted to a band in a machined recess on the barrel, or possibly just a thin steel band that is difficult to discern. The disassembled gun in the inset photo by comparison has what looks like a standard-length 10.5" barrel, but fitted with a device for mounting some kind of attachment, maybe a bipod or possibly a proprietary bayonet. It too has a Model 1923 buttstock.
Good points, but I note the article from the Illustrated London news is dated July 1921, (in the same post which appears to be from the same photoshoot as the undated Mid Week Pictorial), which is approx. 5 months into the production of the Model of 1921's.
I would have thought with the award to Colt for the manufacture of 15,000 Model of 1921's, that AOC would have thought they had perfected the development of their submachine gun design, and would therefore be marketing the 'standard model' coming off the assembly lines at that stage.
As, I understand it, maybe incorrectly, it was only due to lagging sales of the Model of 1921's, that AOC began to look at modifications of the original Model, in an attempt to market the static stock they had.