1. Looking on the voiding perforation I found out that 5th hole from the top (or other side) is bigger in diameter.
As far as I know that type of perforation machinery was never used to make voiding perforation on Soviet stamps.
2. Looking on the first "proof" tank stamp I saw rough perforation, which was ONLY on the latest
(2nd issue) of those stamps.
Can it be on the proof?
3. Colors...
Tanks “proofs” have green & brown colors.
Original stamp was issued in brown.
From the information I have those 2 colors can be chemically received from brown.
Nekrasov "proofs" have orange and brown colors. The one in the middle - sepia - is original (issued) color.
The same story here - both colors can be chemically received from sepia.
4. Design details.
Some of the "proof" lost small details of the design
5. There is no information about such proofs (Ok, shut me here - it can be in some old collection for a years,
nobody saw those before, etc, etc...)
All the above bringing me to the conclusion that those "proofs" were made up for Mr. Koopman.
Now if some of the "proofs" are at least questionable can we believe in other "proofs" from this estate
such as "SPARTAKIADE" (shown above) or another one:
Specialized Catalogue of Postage Stamps. Vol. 5, Part 2. USSR. 1923 – 1940 issued by STANDARD-COLLECTION (known also as ZAGORSKY catalog) in 1999
gives information about proofs and essays of SPARTAKIADA set. No information about proofs with annuling perforation of that type is given. Same about
28-kop stamp from 10th Anniversary of October Revolution. Though it mentiones two other stamps from that set with annuling perforation (but
doesn't show them).
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