20 pesos watermaked RA in sun with wavy rays: 1 Scott number, 5 stamps

In these scans we can tell the difference between the first two papers. The 1E1 was used in 1935 and 1936, and the 1E2 was issued in 1937 (this latter paper is from Austria).

1E1:

1E2:

Then there is the 1E4 of 1940, with the watermark rotated by 90 degrees when compared to the 1E1 and the 1E2.

The last issue with this watermark is from 1951, the 1L1, with colors unique to this printing.

And then there is the clay issue of 1943. The watermark sons are ovals and the clay layer on the front of the stamp is shiny and reflective.