There is only one Henry F Stein in US Marine Corps Muster Rolls 1798-1940. Of the 28 entries the earliest is Oct 20, 1913, no rank so must be enlistment. In remarks is "At Baltimore to MB Norfolk." Western Recruiting Station. On Oct 24th 1913 he is a private and remarks have "ED Cook 4th Class" Looks like he reenlisted Jan 13, 1918 with rank of Corporal - Station Company A Third Separate Battalion, Quantico, VA On Oct 1918 he is a Sgt in "CO B 1st Training Battalion, 1st Training Regiment, Us Marines Apo 727" and listed under "Marine Corps Reserve Class 4" "rank of Sgt auth 10/3/18.13 tr to 2nd Div"Last entry is rank of Sgt Aug 1939 "Marine Barracks, Us Submarine Base, Coco Solo, Canal Zone" No remarks made.
There are 128 Robert Steele entries with different middle initials or middle names. See if your local library has Ancestry to use.