When the Bureau of Engraving & Printing turned over their archive of certified proofs to the Smithsonian in the 1960s and '70s, about 50,000 philatelic proofs went to the National Postal Museum and some 300,000 went to the National Numismatic Collection, housed in the National Museum of American History (NMAH). The reasoning was that anything done in service of the Treasury was more appropriate for numismatists.
However, there are probably more philatelic-related items in the NMAH holdings than there were in the postal acquisitions. These include virtually all revenue stamps, savings stamps, special tax stamps, even NPS Trailer Permit Stamps. There are some really amazing pieces in this collection, which is a researcher's gold mine.
The NMAH began a digitization program 6-7 years ago, to create high res images of about 80 percent of the certified proof collection. These have been available online for some time now, but they are almost completely unsearchable, except for National Bank Notes, which were well documented and transcribed by volunteers.
Fortunately, numismatic writer and researcher Peter Huntoon created a finding tool, which he shared with me. This has a rudimentary breakdown of which items are stored in which boxes, and their scan numbers. I've been going through a lot of the bonds and currency proofs for a paper money forum, but I often veer into the esoteric revenues for fun. I thought it might be fun to share some of the interesting discoveries with the philatelic community, too.
Here's one I found today among the private proprietaries. Apparently, after the Bureau called in the printing plates from National Bank Note Co., all they did was deface the NBNC imprint and add their own. I've seen this on quite a number of M&M proofs now. Here's an example on a 3¢ revenue for GG Green. These stamps have an added curiosity of being printed tete-beche in alternating rows. Any thoughts on why this would have been done?
Here's a link to the proof sheet. To see a close-up, click on the NMAH image and wait for the pop-up to load.https://americanhistory.si.edu/coll...nmah_1624352
If anyone would like to peruse these particular proofs, they can be searched, using the NMAH ID numbers: NU.297219.158999 through 159130.