Here is some more on Steveson.
STEVENSON, W C G L 1st Lt. Chicago --- Mustered out Apr 11, 1864
STEVENSON, W C G L 2nd Lt. Chicago Jun 6, 1862 Promoted Junior 1st Lt. [Nov 19, 1862]
Started out in one company and ended up in Company M.
From the official record of the state of Illinois.