C11 With Odd Numbering?

I have several top strips of 5 of #C11 that have numbers hand stamped onto them. My first thought is they were used for counting or some inventory purpose. However, the number applied to the front does not match the number applied to the back on any of them.
Is anyone familiar with what the reason is behind these? Or perhaps it has nothing to do with a postal service function and was applied by a collector or dealer?
Any input is greatly appreciated!!

HarryG

I have seen them in the selvage, but never on the back of a stamp. Everything I have read about them assumes that they were an accounting number of some kind.

Why the front and back numbers don't match: Sheets of stamps were often stacked in bundles after production. If someone hand-stamped a sequential tracking or ledger number onto the margins of stacked sheets or large blocks, a heavy strike could easily bleed through or transfer offset ink to the back of an adjacent sheet, causing mismatched numbers when the sheets were later separated.


It is highly probable that these numbers were applied after production by a dealer, large estate auction house, or an institutional collection for inventory control. Alternatively, during the late 1920s and 1930s, certain larger post offices or bulk commercial users manually stamped counting indicators on sheet margins to simplify auditing and inventory tallies.

Central City Post Offices: Major metropolitan hubs like New York, Chicago, or Washington D.C. managed massive daily shipments of bulk airmail. Clerks at these central facilities frequently bundled sheet stock and hand-stamped sequential control numbers on the margins for internal auditing and tracking ledger sheets.

The Philatelic Agency: Established by the Post Office Department in Washington, D.C. in 1921, this specific branch fulfilled mail orders for collectors seeking high-quality stamps. They routinely processed full sheets, blocks, and position pieces, often using sequential tracking or inventory stamps during batch handling.

Large Commercial Mailers: Major companies and financial institutions in the 1920s purchased stamps by the hundreds of sheets. Their accounting departments routinely hand-stamped margins to tally sheet usage and prevent employee theft.

Prominent Stamp Dealers & Auction Houses: Famous early 20th-century philatelic businesses (such as J.C. Morgenthau & Co.) regularly processed large estates. They utilized numeric hand-stamps on sheet margins to catalog auction lots, inventory tracking sequences, and specific collection files.

(Per Gemini)