Thanks for the great research, Joe. This article from the December 1, 1941 Card Collector's Bulletin, based on notes made by Harry Lillien from the journal Tobacco (which I guess was distinct from "Tobacco Journal"?), is also relevant here. I'm not sure why Lillien's notes include so few issues, but the dates for the A&G sets he found are consistent with your findings. Walter Corson wrote these dates by the relevant entries in his copy of the 1946 American Card Catalog, which I have. I have a nagging feeling that I've seen another early article like this that includes other dates for N card sets, but if so I couldn't find it earlier.
