Dating those reverse-threaded Conklin crescent-filler sections

As if I weren't busy enough already, I've been serving for some time now as Librarian for the Pen Collectors of America (a venerable nonprofit collector-run organization, well worth supporting -- please consider joining, or rejoining if you've let your membership lapse). If you've not checked out the online Reference Library lately, you are in for a surprise: over the last few years fresh material has been added at a steadily accelerating pace, with no slowing in sight.

A recent addition is the Conklin service manual whose cover is shown above. While preparing the listing I noticed something remarkable: on pages 3 and 8 Conklin's notorious left-handed section-barrel joint is illustrated and described as a newly introduced feature. 

These left-handed four-start threaded sections have long been known to pen collectors, but I've never seen anyone propose a date or proffer any company literature in which they are described. Finding these mentions in a datable Conklin document is therefore a bit of a discovery. "Datable" rather than "dated", however, as the manual has to be dated indirectly. We can start by noting that the San Francisco address shown on the cover was in use no earlier than the very end of 1920, while the listing of the Chicago, San Francisco, and Boston branch offices has to predate September 1922, when London and Barcelona were added. On top of this, we have in the Reference Library a mailing that went out from Conklin to dealers under a cover letter dated January 20, 1921. The mailing was to promote Conklin's service kits, and the flyer included reproductions of two pages from the kit's manual, which correspond exactly with our manual. While it is possible that the manual was published in more than one version, in all likelihood we are looking at just one edition, printed at the very beginning of 1921. This would put the introduction of the reverse-threaded sections towards the end of 1920. How long they remained in production is another matter. To my knowledge they never appeared on any Conklin lever-fillers, nor do they show up on the Endura-era crescent-fillers with flat cap tops. I would guess that this "improvement" was quickly dropped after Conklin was flooded with dealer complaints about broken barrels.