Argentine departmental officials

I noticed that although most departmental officials of Argentina have round
dots between the initials, there are some, particularly Ministry of Justice
and Instruction, which have square dots. Does anyone know whether this was
a deliberate change in design or simply a change of printer? Also, does
anyone have a used copy of Kneitschel's Catalogo de los Sellos Postales de
la Republica Argentina he/she would like to sell? I have tried Ebay and
Yahoo with no success. Thanks.
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Tony V. in Ottawa, Canada