Hello again,
Thanks for your replies Abrac and EnchantedShadow. Sounded good for a while there Abrac, and I relaxed in the knowledge that my decks were from 1917 or older; like yours would appear to be also EnchantedShadow. But perhaps not, as I will explain.
Firstly, my apologies for posting that Peter Endebrock link above without even checking it! - its dead.
But this one works -
http://www.endebrock.de/stamps/st-f.html
...and I now believe the information and images are superior to Kaplan's, especially when considered in the light of the following discovery.
I sourced copies of The Encyclopedia of Tarot vol.1 & 2 to view the pages Abrac mentioned, and found that some of the tax stamp information in vol.2 is contradicted by an image in vol.1 !!
Kaplan states there was no tax stamp used between 1922 and 1940, and yet the Grimaud TdM on p.138 vol.1, which he says is from 1930, actually has the 12 Avril 1890 stamp on the Ace of Deniers*; confirming what Endebrock said about it being (re)used between 1922 and 1940. You have to use a strong magnifier, and even then its a case of looking more at the length of the inscription than the actual words - then compare with the very clear scans on Endebrock's page. There is a distinct gap between the R of Republique and the D of Decret, and again between the 0 of 1890 and the last e of Francaise, but there is no such gap on the two subsequent tax stamps, (because their inscription is longer), so it has to be the 1890 stamp on Kaplan's 1930 Grimaud TdM. And it is a 1930 deck because, using the magnifier again, you can clearly see that Le Bateleur has two coins rather than dice on his table.
Therefore, this raises the question once again, just exactly how old is a deck with an 1890 stamp? I guess the back design is a bit of a clue Abrac, but hardly definitive, and I'm stating to feel that twinge of disappointment returning.
*as does the Dusserre repro I might add!