Headstamp identification

Hello all,
I am new to this forum and to ammunition collecting. I recently purchased some US caliber .30 ammo for my WWII collection. I have been able to identify the manufacturing locations TW (Twin Cities) and SL (St Louis) but I am confused by the date stamp on the SL cartidges. It is just a 4. Does this mean 1944 or something else? Any responses are appreciated.

Yes it is 1944, the 3 in a 43 hs bunter was ground out and bunter reused as an economy measure.

Steve–The same thing was done for the 1955 cartridges. The “54” bunter had the 4 removed.