English concertinas by Wheatstone are dated from the digitised factory ledgers, sometimes to the day. Lachenal dates are formula-based estimates; English numbers ran separately from Anglos.
On the right-hand end plate or an internal reed-pan label. Markings and exact positions vary by maker and era — the serial number guide covers the common locations for every instrument.
6 makers with 411 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.