Always nice to be remembered :-)
I do remember some of the correspondence I had with Brain about the E220 backs years ago. I seem to recall I was measuring the back lines in millimeters at the time and also found some backs in my collection to be reversed. Because I am easily confused and I'm pretty tired, for the sake of this discussion the 'B' below the first 's' is type 1, 'B' below the second 's' is type 2? If yes, then here are some verifications to Brian's type 1 list from my own collection:
Gowdy
Rousch
Grimm
Hollacher
Picinich
Burns, CLE
F Snyder crouching
F Snyder standing
Johnson
Frisch
Kilduff
E Meusel
In total, I have 85 of the type 1, 2 of the type 2 back and 21 of the type 2 upside-down backs. I also have a handful I can't identify. Are the 'normal' type 2 backs 10x as difficult as the 'upside-down' type 2 backs? And are those upside-down type 2 backs 4x as difficult as the type 1 backs? Probably not based on my meager sample but the disparity is interesting.
Here are some pics of dupes I have with different backs...
Frank Snyder standing with type 1 and type 2 backs...
e220fsnyderfront.jpg
e220fsnyderback.jpg
Zach Wheat with type 1 and type 2 upside down backs...
e220wheatfront.jpg
e220wheatback.jpg