Brian,
Nice research. You may want to consult an OC article from 2007 (Issue 11) that does an extensive analysis of these sets. I agree that the initial distribution date for the early two sets--Brunners and Fleischmann's-- is most likely 1912 for reasons you have stated.
I did see a few ads for Martens and Weber Bakeries in the 1913 and 1914 papers from newspapers.com, and there was no mention of the cards:
As you can see, there was an ad for some sort of game [insert dirty joke here], so the bakeries should not have been averse to advertising the cards. No luck so far, although there are obviously other newspaper sites. Note that the Martens bakery appears to have been located in Jersey City, if that was not known already.