Sources
Where each decoder’s rules come from. Last reviewed 30 September 2026.
How we decide what goes in
Rules come from the brands where they publish them, and otherwise from resellers and auction houses; where we rely on collector databases (Seiko caliber years, the Omega and Speedmaster year tables) the page says so, and that data never rules a reading out. The same text copied across three sites counts as one source.
Before a decoder goes live we run it on genuine pieces: for Hermès, Omega and Cartier on pieces with known dates where we could find them, for Seiko on dated auction lots, for Coach and Gucci on listings from resellers that authenticate what they sell. The test we care about most: could someone holding a genuine piece get an answer that reads as a warning? If yes, the wording changes. When the evidence runs out, the decoder says so instead of guessing.
New Hermès year letters are added once two independent sources confirm them.
Hermès date stamp
Year letters 1945–2025 agree across at least five reseller guides; the 2026 letter (G) is in three guides and on dated listings. The 2015–2026 letters are confirmed on dated listings from two resellers (32 stamps, 1973–2026). We have no dated bags from 1945–1970, so those years are shown as approximate. Hermès publishes no table and authenticates only pieces bought through its own stores and website.
- Brand Hermès – authentication FAQ (archived copy, 2 March 2026)
- Reseller Madison Avenue Couture – date stamp guide
- Reseller Rebag – Hermès stamps by year
- Reseller Fashionphile – reading Hermès date stamps
- Reseller Fashionphile – Hermès stamp symbols
- Reseller Privé Porter – how to read your Hermès date stamp
- Reseller Xupes – guide to Hermès date stamps
- Reseller Love Luxury – Hermès stamp guide
- Reseller Randolph – 2026 Birkin price update (2026 letter)
- Auction Sotheby’s – Balle de Golf listing noting no blind stamp
- Test set JaneFinds – dated Hermès listings
- Test set SW3 Boutique – dated Hermès listings
Coach creed
Coach has never published a key. The 1994–2006 reading comes from collector guides that agree with each other; dozens of ShopGoodwill listings sold with authentication certificates show the same formats, though none states a year. We test on listings from resellers that authenticate what they sell. Model names come only from Coach’s own product pages, for a short list of current styles.
- Brand Coach – product pages with “Style Number” (UK storefront)
- Reseller ShopGoodwill – creed codes on certified listings
- Reseller ShopGoodwill blog – Coach serial number guide
- Reseller Essex Fashion House – Coach 1941 and sample listings
- Collector Coach Bag Rehab – dating vintage Coach
- Collector Valentina’s Vault – the Coach creed
- Collector LegitGrails – Coach serial number checker
Gucci style number
The list is the bag and travel styles in gucci.com’s US product sitemap on 30 September 2026. Gucci publishes no guide to the leather tag; the reading of its two lines comes from resellers. The tag carries no date, so we test on listings from resellers that authenticate what they sell.
- Brand Gucci – US product sitemap (via robots.txt)
- Brand Gucci – Authenticity Tag (NFC) page
- Reseller Dallas Designer Handbags – listings with tag codes
- Reseller Rediscover Vintage – vintage Gucci listings with codes
- Reseller Attic House – Gucci listings with both tag lines
- Reseller Yoogi’s Closet – Gucci tags and serials
Seiko serial
Seiko publishes no table. The reading is consistent with about 90 Bonhams lots from 1964 to 2019, though their circa dates may themselves come from the serial. Caliber production years come from a collector database (WatchSleuth), are approximate and never rule a reading out.
- Brand Seiko – customer service FAQ
- Brand Seiko USA – watch registration (limited-edition numbers)
- Brand Grand Seiko – registration search
- Auction Bonhams – Making Waves: Seiko, part 1
- Auction Bonhams – Making Waves: Seiko, part 2
- Dealer Gnomon Watches – where Seiko watches are made
- Collector Plus9Time – Seiko caseback information
- Collector WatchSleuth – Seiko date finder and caliber table
Omega serial and reference
The year table and the separate Speedmaster table (Roman Hartmann) are collectors’ tables; Omega doesn’t publish one. We checked the year table against 39 watches from 1941–1978 with archive or catalog production dates. We found none from 1980–2007, so that part of the table is less certain. The reference layout is Omega’s own.
- Brand Omega – FAQ on serials and the reference codification
- Brand Omega – conditions of sale (archive extract)
- Dealer Bob’s Watches – Omega serial number table
- Auction Bonhams – Speedmaster ST 145.022 with archive date (1976)
- Auction Bonhams – Moonwatch 310.30.42.50.01.002, 2021, number in the 83 million range
- Collector Roman Hartmann – Speedmaster production table
- Collector OmegaForums – serials starting with a letter
Cartier reference
Model names come from references in Cartier’s current catalog (site sitemaps, 30 September 2026). We show no year: the “first two digits” rule failed on dated Bonhams lots.