Anglo concertinas by Wheatstone ran a separate 5xxxx series after 1938 — never mix it with the English/Duet run. Crabb and Jeffries Anglos are dated by ID ranges and label addresses.
On the right-hand end plate or an internal reed-pan label — Anglo ranges ran separately from English/Duet. Markings and exact positions vary by maker and era — the serial number guide covers the common locations for every instrument.
6 makers with 374 dating ranges are listed on this page. Coverage grows as more maker records and historical tables are verified.
Recheck the characters exactly as marked — letters and leading zeros are part of the number. On several makes the stamped numbers are internal assembly or importer codes that cannot be dated; some production periods are simply not covered yet.