Yup....this discussion is definitely geared towards my addiction of T206 backs - I think that I've checked the thread four times today for updates
I agree that the Cobb/Cobb is a tough decision. If it were included I'd probably place it at #1 on the list. Although the total number of known Cobb/Cobb examples (14 or 15) known likely exceeds the known number of OM or Lenox brown cards - I find it not only possible but likely that several undiscovered examples of each exist. In fact, the OM brown in my collection was purchased by my dad many years ago and no special mention of the color was made. I don't think that a Cobb backed card would (or could) ever fly under the radar.
I would personally vote for the Cobb/Cobb to be included - I am biased though. This is probably the toughest call of all to make.
What a fun topic !!
-SGL