Pettigiani refers to December 1939 as the first printing of the 1c Sarmiento in offset-litho on Holandés [it is rather German paper from Stinnes's paper mill in Hillegossen, Germany].
The scans so far show an earlier date - October 1939 - for this!
But now!
10.08.1939
and
??.09.1939
to be continued ...