[x2drich2000]

We've had the discussion before, but I can't seem to find the thread. Short answer...there is no way to actually tell. Long answer...I think E92 makes the most sense in most cases based on circumstantial evidence.
- we can eliminate several sets due to specific card characteristics (E105, E106, D303, some T216, etc).
- From the known blank backs (there are more, but Chase, Crawford, Davis, Dougherty, Gibson, Kleinow, Knight, Lajoie, Magee, Mathewson, McGraw, McLean, Miller (fielding), Schlei, Seigle, Smith, Tinker, Wagner (throwing), Zimmerman), several players/poses do not exist in all sets including E90-1 (Crawford, Davis, Lajoie, etc)
- Prize Fighter & Menagerie backs - Magee (Prizefighter) and Murphy (Menagerie) are both not in E90-1.
- E92, particularly Cocoa, is riddled with print errors (miscut backs, upside down, miscut fronts, misaligned backs, missing color passes, etc. Based on this I believe having a blank back would be expected and very possible. E101/102 we don't see these issues, at least not to the same degree as E92.

With all that said there is also 1 blank back (Krause) that can only be from E90-1 so obviously we can't say definitively which set they come from.

To further complicate things, there are also blank back T216 including Miller that originated as a group and were brought to auction by Goodwin. If I remember correctly these were found with other T216 and could be identified as different based on the card stock and subtle nameplate variations in some players.