Other possible memberstates:
(Outer) Mongolia
DPRK
Jugoslavia
Afghanistan
Cuba
I think these are all unlikely candidates, apart from 'Yugo Disney'. Finland would be the most plausible additional WP member state. This could come about one of two ways -
- Red victory in Finnish Civil War of 1918
- Total Soviet victory in Winter War of 1939/40 and/or Continuation War of 1941-44