Look on the movement for thr serial number.
All 992B movement serial numbers start with the letter C. This serial number can be found on the movement (not the case).
C001-C13000....... 1940
C13001-C37900..... 1941
C37901-C62800..... 1942
C62801-C87700..... 1943
C87701-C112400 ... 1944
C112401-C137500... 1945
C137501-C175000... 1946
C175001-C199800... 1947
C199801-C254500... 1948
C254501-C281400... 1949
C281401-C310200... 1950
C310201-C352800... 1951
C352801-C385800... 1952
C385801-C408300... 1953
C408301-C415500... 1954
C415501-C423600... 1955
C423601-C441700... 1956
C441701-C448400... 1957
C448401-C455000... 1958
C455001-C461700... 1959
C461701-C468400... 1960
C468401-C475000... 1961
C475001-C481700... 1962
C481701-C488400... 1963
C488401-C495000... 1964
C495001-C501700... 1965
C501701-C508400... 1966
C508401-C515100... 1967
C515101-C521800... 1968
C521801-C525300... 1969
All 992B movement serial numbers start with the letter C. This serial number can be found on the movement (not the case).
C001-C13000....... 1940
C13001-C37900..... 1941
C37901-C62800..... 1942
C62801-C87700..... 1943
C87701-C112400 ... 1944
C112401-C137500... 1945
C137501-C175000... 1946
C175001-C199800... 1947
C199801-C254500... 1948
C254501-C281400... 1949
C281401-C310200... 1950
C310201-C352800... 1951
C352801-C385800... 1952
C385801-C408300... 1953
C408301-C415500... 1954
C415501-C423600... 1955
C423601-C441700... 1956
C441701-C448400... 1957
C448401-C455000... 1958
C455001-C461700... 1959
C461701-C468400... 1960
C468401-C475000... 1961
C475001-C481700... 1962
C481701-C488400... 1963
C488401-C495000... 1964
C495001-C501700... 1965
C501701-C508400... 1966
C508401-C515100... 1967
C515101-C521800... 1968
C521801-C525300... 1969