[oldjudge]

Todd--Thanks for posting, and thank you and Tim for publishing the wonderful research that you did. Personally, I believe that the printing date is the key. Since M101-5s were printed first they get my rookie vote. Looking at issue date is always tough, especially with blank backs. I think many blank backs we see today, not just Ruths but all M101s, were not issued during the period but were from uncut unissued sheets that were cut up later. Why do I think this--compare the average grades for ad back cards and blank back cards. The blank back cards are significantly higher. Since everything else is equal, the lower wear on them probably translates to less time in circulation.
As to that April 6, 1916 TSN ad for M101-4s, was Mendolsohn advertising to potential companies to use his cards for advertisement, or was he marketing the cards to the general public? If the latter,doesn't it seem strange that he is directly competing with the companies that he just sold ad back printing to? I don't have a copy of the ad in front of me--if I did the answer might be apparent.
On a side note, the closeness of the April 6 announcement and the Famous and Barr issue date may explain the mixed nature of the Famous and Barr set. It seems that Mendelssohn already had printed some M101-4s before Famous and Barr got their cards. Perhaps the first shipment to Famous and Barr was an error--they should have been getting the M101-5s and numbers 1-20 came as M101-4s. This was corrected on subsequent shipments, so that the rest of the set is M101-5s. Since this is the mirror image of the Herpolsheimer set, I guess another possibility is that the packages got screwed up and Herpolsheimer first shipment was sent to Famous and Barr and vice versa. Is this what you think?