This story would explain why Christopher Zakiyan, in his book Armenia: Postage Stamps, Fiscal Stamps, Postage Cancels (Yerevan 2003, pages 63ff)lists Soviet fiscal overprints on only the 1,5,10 and 15 rouble Chassepot stamps, which are also the only values which appear on the documents he illustrates (There is an unexplained mystery about what happened to the 3 rouble Chassepot stamp).
Some of those documents were subsequently "enhanced" by the addition of fiscal stamps, sometimes genuine stamps, sometimes fakes. For example, I have seen a fake fiscal overprint on a 10 rouble Chassepot REPRINT attached to an authentic document. Such a pity: a nice document and a crude fake!