Bayan and garmon makers of the Soviet era (Tula, Shuya, Kazan) did not publish serial tables, and their numbers were not chronological: look for the ОТК stamp and construction features.
Inside the right half-body; look for the ОТК quality stamp, which often carries the year. 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.