| Value | Category |
|---|---|
| 00 | 1900 or earlier |
| 01 | 1901 |
| 02 | 1902 |
| 03 | 1903 |
| 04 | 1904 |
| 05 | 1905 |
| 06 | 1906 |
| 07 | 1907 |
| 08 | 1908 |
| 09 | 1909 |
| 10 | 1910 |
| 11 | 1911 |
| 12 | 1912 |
| 13 | 1913 |
| 14 | 1914 |
| 15 | 1915 |
| 16 | 1916 |
| 17 | 1917 |
| 18 | 1918 |
| 19 | 1919 |
| 20 | 1920 |
| 21 | 1921 |
| 22 | 1922 |
| 23 | 1923 |
| 24 | 1924 |
| 25 | 1925 |
| 26 | 1926 |
| 27 | 1927 |
| 28 | 1928 |
| 29 | 1929 |
| 30 | 1930 |
| 31 | 1931 |
| 32 | 1932 |
| 33 | 1933 |
| 34 | 1934 |
| 35 | 1935 |
| 36 | 1936 |
| 37 | 1937 |
| 38 | 1938 |
| 39 | 1939 |
| 40 | 1940 |
| 41 | 1941 |
| 42 | 1942 |
| 43 | 1943 |
| 44 | 1944 |
| 45 | 1945 |
| 46 | 1946 |
| 47 | 1947 |
| 48 | 1948 |
| 49 | 1949 |
| 50 | 1950 |
| 51 | 1951 |
| 52 | 1952 |
| 53 | 1953 |
| 54 | 1954 |
| 55 | 1955 |
| 56 | 1956 |
| 57 | 1957 |
| 58 | Two years |
| 59 | One year |
| 60 | Less than one year |
| 65 | Always |
| 68 | Transient |
| 98 | Unknown |
| 99 | NIU (not in universe) |