Below are selected Buenos Aires 21 images. Here is a link to the main Buenos Aires Numeral Postmarks page. Illustrated below left are two 10cR specimens. The top specimen is a 10cR1E postmarked in December 1935, and the bottom specimen is a 10cR1Et. Below right is a 50c stamp also showing a Buenos Aires 21 postmark. Notice that these three specimens show three different formats for this postmark.

Below is a late use of this postmark.