Pieces are date coded by mark and by code. Though some of the earlier pieces may be marked with an easy date code of a 4 digit code which represents the full year. Some of the other earlier pieces and later pieces are marked with either a single or double digit number (dash) double digit number or a letter (dash) double digit number code. Knowing that Bailey-Walker marks are pre 1942 and Walker marks are post 1942 will help identify which code to use.
1923-1942: Bailey-Walker mark - Four digit number codes might represent the year produced.
Year/Month
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
January-December
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
Year/Month
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
January-December
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1923-1942: Bailey-Walker mark - a single or double digit number(dash)double digit number code is used. The first single digit number of 1-12 represents the month of January to December. The second double-digit number represents the year.