Paul I'm not certain about this but I have a list of Hardy rod numbers that someone gave me donkeys years ago.
It starts at rod Number 13452 in 1890 up to rod number 101679 in 1904.
Then they started with A prefix in 1905 up to rod number A100150 in 1916.
B prefix in 1917 with rod number B1021 up to rod number B23556 in 1919.
C prefix in1920 with rod number C10405 up to rod number C25725 in 1922.
D prefix 1922-3 with rod number D171 up to rod number D7375 in 1925.
E prefix started 1925 with rod number E1045 right up to E98999 in 1955.
Note Prefix F and G are missing.
H prefix in 1956 with rod number H101 right up to 1966 on rod number H69100.
After 1966 a different code was used where each year had a different Prefix letter.
The F prefix doesn't look to have been used at all unless it was kept for fibreglass rods (that's just a guess by the way) but I was told the G prefix was used for rods containing mixed sections such as cane / split cane and maybe even greenheart and these rods cant be accurately dated.
Probably totally wrong but I thought I would share as it may help somewhere along the line. Or more than likely bring more confusion.
Wal.