Source-backed
Dates, institutional roles and production-process claims tied to the records below.
Sources & evidence
Sources, evidence & rights
See exactly which claims are source-backed, which statements are editorial synthesis, and what media this release deliberately did not use.
Evidence states
Labels do work.
A source link does not turn every sentence on a page into a sourced fact. This release distinguishes directly supported facts from explanatory synthesis.
Newly authored explanation
Taxonomic framing, learning sequence and cross-page comparisons created for ICU from the available evidence.
Not claimed
No market values, rarity rankings, condition grades, provenance claims, ownership history or global completeness are asserted.
Source ledger
Smithsonian National Postal Museum — Great Britain — International Philately
Used for: Penny Black issue date/context; postal prepayment reform.
Smithsonian National Postal Museum — The World's First Postage Stamps
Used for: Penny Black validity date; design/production context; sheets of 240.
Smithsonian National Postal Museum — Printing and Production Equipment
Used for: intaglio process; flat-plate and rotary printing workflow; gumming/perforation as production steps.
Smithsonian National Postal Museum — Tools of the Hobby
Used for: perforation gauges; watermark detection; magnification and identification practice.
Smithsonian National Postal Museum — Marking Devices
Used for: postmark vs cancellation distinction; postal history markings.
United States Postal Service — Citizens’ Stamp Advisory Committee
Used for: committee established in 1957; subject recommendation and artwork development context.
Royal Mint Museum — William Wyon & the Penny Black
Used for: Wyon portrait lineage; Perkins Bacon printing context; 1840 validity.
Media rights. No external stamp photographs or scans were copied into this release. The teaching stamp diagrams are original interface graphics, intentionally fictional and labeled as studies. That avoids implying that an issued design is public domain merely because the physical stamp is old.