[judsonhamlin]

I have enjoyed the give and take on this debate and I've given it some further thought, so here is my take and the rationale for my opinion.

T206-1 should represent all White Bordered ATC products issued in the 1909-12 era including T213-1 Coupon and T215-1 Red Cross - both ATC issues during this time frame.

My rationale for the T213-1 follows Ted Z.'s line of reasoning, so I won't rehash that at length here. I will add that the different T216 Mino backs were lumped in the ACC, even thought the paper stock varies among the backs.
With regard to the T215-1, I believe that the rationale against inclusion is not terribly strong. The two most cited reasons (in this thread) seem to rest on the Griffith team change and the listing of "100 subjects". Neither seem dispositive. The team change issue is not dissimilar to the Demmitt/O'Hara St. Louis issues. While Griffith's team change was late in the distribution period of this issue, we have precedent and, we also have several cards where one pose was issued with a player's new team without "redoing" the previous card (e.g. Ball, Willis, Kleinow). Griffith (Wash.) could be considered in the same group as Smith (Chi. & Bos.) or Kleinow (Bos.). Again, Ted Z. has shown the back availability for these cards, so not printing a card with each new back is not inconsistent with cards within the existing T206 framework.
With regard to the "100 Subjects" issue and, for that matter, the horizontal layout, the variety within T206 backs as currently constituted includes several distinct variants (Hindu, Polar Bear, Carolina Bright), so one more design shouldn't upset the apple cart. Further, T206 backs don't always designate a specific number of subjects, and, at least within a particular back, are not accurate (e.g. there are not 350 different Cycle-backed cards). Without a "smoking gun" like a letter between ATC and ALC (like the Uzit), much of this remains speculative, but I believe it to represent substantial proof in favor of inclusion.
Moving forward with what I recognize to be a more controversial position, it is my gut feeling that T213-2, T214 and T215-2 should be joined together for many of the same reasons that have been set forth in this thread. The single proviso would be if all three brands were under common ownership at the time of issue. If so, then join them in one set; either as T206-2 or another single designation. T213-3 should, based upon date of issue, could be listed as T206-3.
Lastly, with regard to the perceived sanctity of Burdick's decision-making, I would only note that he wasn't Adams or Jefferson and we have amended the Constitution. Precedent is persuasive, but never binding - Brown v. Bd. of Ed. and dozens of other Supreme Court cases speak to that better than I can.