For a long time I have been aware that these two plates were cleaned with an acid bath during the CL2B printing of 1952. From looking at several specimens, it is likely that more than one bath took place, especially for the 2 pesos. At this point in the study, I will focus on the difference between the acid-washed printing and the early printings (1936/37). Here is a 50c1E2-SO from 1937.
Here is a 50cCL2B-SO from 1952.
This comparison of the top left corner shows the widening of features that occurs after an acid bath.
This comparison shows the left 50 before and after the acid bath.
Here is the 2P from one of the 1E printings, most likely the 1E1 of 1936.
Here is the 2PCL2B of 1952.
Notice the widening of ARGENTINA...
...and of FRUTICULTURA.