If you really got into this you would find that the so-called confessions themselves are forgeries created by a couple that hated de Cherisey. In the first place there were three parchments, one of which had a coded message on each side. The other two contained very important genealogies, because of which they drew the attention of British agents. If you read some of de Cherisey's earlier letters you would see his intentions were indeed honorable.
One important evidence for the authenticity of the Shepherdess Parchment (created before 1905) is the fact that the tombstone the 128 letter anagram came from had errors created on purpose to make the anagram work. In other words the tombstone was created for the purpose of the anagram! Although the tombstone has since disappeared a copy was made in 1905 with all the errors by an accredited historical source, SESA, of which I have a copy sent by them, in good faith, to me which also includes the whole excursion. My copy is in French and has been translated to English. The tombstone was for a Marie de Blanchefort who died in 1781. Explain to me how or why, SESA in 1905 could have been privy to a hoax in the 1950's, 60's. Although I have seen attempts at this, in the end they do not work.
Another equally important point is the Poussin work itself. Created in the 1630's with, lets call it an alleged code, in the 1750's a copy, the Shugborough(albeit with a few changes), was created with an obvious code. Evidently the creator (designer) of the Shugborough had some knowledge of the earlier Poussin Code. It is a fact that Poussin was known as the keeper of secrets.
Something else that should be mentioned is the Tenniers which seems to get little attention. As I mentioned earlier the "no-temptation" is meant for the Poussin not the Tenniers, but the Tenniers is referenced by the "cross" and the letters "PAX". In the Tenniers is a map and the obvious "Horse of God" that indicates the correct version.
Cheers, Loki