Geno,
I think your point is valid, but
The ad backs on the T206s might be analogous to Burger King putting different promos on their cards for burgers, fries or milk shakes.
I think the more valid argument would be to compare the difference in set designation between the T206s and the T212s. Why don't we consider the 1909 150 subjects as T206-1, like the T212-1 Obaks, etc. It seems like the definition was arbitrary back then (or in Burdick's time) with sets that were contemporary, leaving the modern set definition out of the argument.
I find the Obak comparison more germane to your argument than the 78 set. Topps defined their own sets. ATC never did, we define them (or Burdick did) and obviously not all the same way.
Please accept my apology for my initial post, but it was late and I was thirsty.
By the way in the late 1930s my Dad worked for the same company in Syracuse where Burdick worked, Crouse Hinds. They made all the switches for traffic lights back then, I believe. Now there's a hobby connection that may be unique.
Cheers!