The Cal .30 M1919 Gallery Cartridge (far right in photo below) was intended to be reloaded in the field and so boxes of empty cases were packed and distributed by Frankford Arsenal. The use of second-class and fired cases was also authorized, which accounts for many pre-1919 headstamps.
Boxes of empty cases were like boxes of chocolates. You never knew what you were going to get. The June 1922 box shown below was filled with fired cases that had been re-sized with case mouths chamfered, ready for priming, powder charge, and bullet. This one box contained the following headstamps:
USC Co 17
RA H 17
WRA Co 17