I was going mainly from memories of indexing the service newsleter articles, which may be a bit fuzzy as I continue working back through time and thousands of articles. I'll revist the articles from 1942 on and update my index entries, if needed.
Meanwhile, the site's archive presently includes a
Transmission and Overdrive Serviceman's Training Booklet from 1948, and an
Econo-Drive Serviceman's Training Booklet from 1946. The latter mentions "Econo-Drive in the opening paragraph, but simply refers to the unit as "overdrive" from then on.
So, it looks like they did revert to the "Econo-Drive" moniker for 21st Series, then simply called it as "Overdrive" for 22nd Series on. Apparently the term "Aero-Drive" wasn't a hit with customers.
Yet, there's also a
Borg Warner Overdrive Manual listed under "Service, Shop & Training Manuals"
(though the page header for the article shows "Owner & Operation Manuals"), covering R-10 and R-11.
R-10 is new to me, but I'm a V8 guy - not at all familiar with differences between R-9 amd R-11.
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