Rein, where is the extension hole and
what does perforated with a sheet block mean ?
The single perforation-hole at the left between the "LL" - usually such "extension hole" would be repeated all along the left margin of the sheet suggesting that a horizontal comb-perforator was in use. It seems to me that a complete sheet of 10x10 was perforated in ONE blow. Of course this is a speculation that no doubt could be supported or not by Italian specialists.
What are you trying to show in the two images
below the NRM letter?
I got this extra sheet with the two images as an attachment to their letter and the remark that this should explain the way they worked...
So this Dutch firm "Nederlandsche Rotogravure Maatschappij"
improved and was responsible for innovations in the
photogravure process ?
And NRM in partnership with Goebel who manufactured the
printing presses, then either printed the actual stamps
as for the two Swiss stamp issues 1927, 1928 or helped the
Mexican, Argentinian and Italian (IPS) printers in
developing this process?
The Swiss stamps were printed in Leiden by the NRM but probably perforated in Switzerland.
The NRM helped Goebel in developing and promoting their narrow cylinder reel-fed presses [photogravure, recess] they started to sell since 1928. The history of that cooperation has never been written to some extent although some of it may be found in South African literature about the "Darmstadt Trials" .. I will get back to that and most likely Glenn also may do so...
But NRM had also printed stamps for Egypt in 1923 and
for Peru in 1924?
Apart from that there are many more trials and essays of the 1923-1945 period with lots of countries involved. I had a look at their archive material just before the merger of the NRM and Spaarnestad. After my visit everything got out of sight and nobody now knows what happened to it! The Dutch Postal Museum in The Hague refused to help me in saving the NRM material as it didn't have anything to do the Netherlands Philately so they said...
Did NRM also have anything to do with the Mexican 1917
NO! Too early! The NRM started a weekly coloured magazine called Panorama in 1913 printed in photogravure all the way!
When did NRM begin aiding Enschedé with their
They did not at all! There was NRM instructing Harrison and Sons just before the 1923 Egypt stamps.
I'm just trying to get some sort of timeline for all this.
Also it appears that the Nederlandsche Rotogravure Maatschappij
had the same type of partnership/arrangement with Goebel,
as did Giori with Koenig & Bauer.
Looks like it!