I have taken the time to scan many of the 20 pesos and I have been able to find a plate variety that either is found in different stages as separate plate varieties, or is progressive.
Pettigiani describes it as "retouched upper left corner of the center design and joint cotton bulbs at top."
Here is a link to ALL of the images (400+) in case you want to study them.
https://photos.app.goo.gl/KBAyJ9VEBkVatW7R6
This variety is only found on the 20pNGR (grid unwatermarked paper of 1945)
I find this dot in all of these stamps. It is common to the three variants.
Here is this plate variety over the 20pNGR 'servicio oficial'
