There are two types of M57 pistol.
Type1 - Police and Military
Type 2 - Commercial .
Both types have different serial numbers.
For Police and military serial numbers as follow:
Production Year.........Qty...................Serial Number
1963..........................6,500....................0001-A – 6500-A
1964..........................12,500...................6501-B – 19000-B
1965..........................13,000...................C-19001 – C-32000
1966..........................13,000...................D-32001 – D-45000
1967..........................13,000...................E-45 001 – E-58000
1968..........................13,000...................F-58 001 – F-71000
1969..........................19,000................... G-71001 – G-90000
1970..........................19,000...................H-90001 – H-109000
1971..........................19,000...................I-109001 – I-128000
1972..........................4,000.....................J-128001 – J-132000
1973..........................8,000.....................K-132001 – K-140000
1974..........................8,000.....................M-140001 – M-148000
1975..........................19,000...................N-148001 — N-167000
1976..........................19,000...................N-167001 – N-186000
1977..........................19,000...................N-186001 – N-205000
1978..........................19,000...................N-205001 — N-224000
1979..........................19,000...................N-224001 — N-243000
1980..........................19,000...................N-243001 — N-262000
1981.......................... 4,000...................O-262001 – O-266000
1982..........................4,000...................P-266001 – P-270000
Police and Military also had been buying commercial type of M57 for their services and kept the commercial serial numbers.