Polish stamps were overprinted S.O. 1920 .
In 1920 Czechoslovak stamps were overprinted SO 1920 for use in Cieszyn Silesia , an area disputed between Czechoslovakia and Poland .
Poland stamps were overprinted S.O. 1920 .
In 1920 Czechoslovak stamps were overprinted SO 1920 for use in Cieszyn Silesia , an area disputed between Czechoslovakia and Poland .