Hello
I have doubts about the correct year of the El Salvador banknotes because the banknotes have a date on the obverse and another on the reverse.
The one on the reverse is the date of the Superintendency of Banks and Financial Institutions, and it is subsequent to the date on the obverse.
I believe it would be correct to consider this the correct date as the print does not go into circulation all at once. I understand that you are following the Pick organization but I think the catalog did not make a good decision
At Exemple I have a banknote of 1972 / 1976.
At this eg. I agree that is a Banknote Date: 19-AUG-1976, with Plate Date 24-OCT-1972