Here are two Paraguay postal history items that I find fascinating.
The first is a cover mailed from Viletta on 27 June 1909. The envelope is a piece of Argentina postal matter, the item was mailed to China, via Siberia, the rate was 15 centavos. The 15 centavos rate was for printed matter and was paid for by a 10 centavos stamp and a bisected 10 centavos stamp. (Bisects were not authorized at this time but often were accepted.) The Argentine envelope has an open oval at the upper right to show that the contents were really printed matter. Shown also are the Buenos Aires transit marking and the Shanghai Local Post marking.
The second cover also has a bisect. It is the 2c issue of 1901-02 and was used to pay the printed matter rate. Some collectors might pass this by because of the lower-left corner of the envelope being cut off. However, that would be a mistake as this was a method used to show that the contents were really printed matter. Thus, it is not a damaged cover but one proving that the attached stamp was used to pay the printed matter rate. Also note the “Estafeta No. 9” cancel of Asuncion.