[RCMcKenzie]

Okay, here's what I've found...

There are 3 different back types, 5 different backs including litho companys.

I'll call them
A1 Leading Baseball Players- Giles & Liberty
A2 Leading Baseball Players- Donaldson Bros.
B Police, baseball, actors, jockeys - Julius Bien
C Police, baseball, actors, jockeys, chiefs of fire depts- Donaldson Bros
C2 " " -Ballin 1888

A1 Giles is only found in the "generic subset"
A2 Donaldson is only found in Lipset's "all the rest subset, or like images"
B Only found on most Browns cards, and actors and Jockeys and captains
C Found in all 3 of Lipset's subsets
D Only found on "type 2" Police captains

Here is the checklist coded by back so far. I'll post scans that I made later on.