https://thecabe.com/forum/threads/serial-number-and-date-code-information.71542/#post-441223
Morrow Coaster Brake Hub:
Letter and number note the year and quarter of production.
Example: I 3 = produced 1939 July-September
Note: many hubs are marked 36-13, this is not the date code, it notes the # spoke holes and size.
A - 1931
B - 1932
C - 1933
D - 1934
E - 1935
F - 1936
G - 1937
H - 1938
I - 1939
J - 1940
K - 1941
L - 1942
M - 1943
N - 1944
O - 1945
P - 1946
Q - 1947
R - 1948
S - 1949
T - 1950