Awesome writeup Mark!
So a couple of remaining questions:
1) Which Supplements are possible with an ad-back? It seems like the ad-backed Supplements were of ones already issued that they must've had extras of. Since none were available of #1 Bresnahan, #3 Mathewson, #4 Cobb, #5 Lajoie, #8 Walsh, #10 Wagner, #35 Cobb/Wagner, and #49 Cole, we can probably assume they wouldn't have ad backs. #2 Young/Criger, #7 Chance, #9 Rucker, #11 Jennings, #17 The Pirates, #18 The Tigers, #38 Plank, #39 Johnson/Street, and #51 The Athletics, as you mention, weren't available by the 3rd ad-back so a guess may be that we may not find those either with ad backs since the supply may have already been low to begin with on those and they went fast. With #55 Wallace (printed 21-Dec-1910) being the earliest known with an ad back, there is probably a good chance that none predating this very much will surface.
2) Distribution method for the advertisements? So perhaps they took some of the Supplements, threw ads on the back, and included them in future issues of The Sporting News? Or put them on newsstands? One thing they all seem to have in common are the two vertical and two horizontal fold lines. Why would they have been folded in such a way? Perhaps they were included in some sporting product like ball gloves or baseballs?
3) Why is #49 Cole not available in the first ad-back release but it is available in the 2nd release?
Thanks again for the interesting writeup!
Rob
