Vatican City Scott 35-40 Overprints/Surcharges

Curious if anyone has information on a resource to identify forged overprints in this series? Scott 2015 only states "Forged surcharges of Nos. 35-40 are plentiful" which is not exactly helpful.

In addition, the photo showing a sample overprint shows a period, not a comma on all of the surcharges, but the verbiage in the listing indicates commas.

Have searched high and low on the web for any information but to no avail.

The reference photo is from a current listing that has a cert from a German organization that I'm not familiar with.

Much appreciated.

The Philatelic Foundation has a short article on these provisionals in their Opinions IV volume. Here is a link to the Table of Contents:
https://www.philatelicfoundation.or...inside-view/

Click on the text "Link to Publication" and go to page 232.
No doubt there must be newer articles but Vatican City is not my field.

Thank you Germania; very informative and much appreciated.

See https://www.vaticanstamps.org/VPS/s...?query=35-40

Thank you as well Jogil, also very much appreciated.