Chromatic button accordions share the Hohner and Italian maker traditions. On Soviet-era bayans the number itself does not date the instrument — the internal ОТК stamp does.
On the rear body, the bass side, or inside on the reed-block frame, depending on the maker. Markings and exact positions vary by maker and era — the serial number guide covers the common locations for every instrument.
2 makers with 202 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.