Quote

Ensign ------ Barron, of the 1st Royal Garrison Battalion, to be Adjutant to the Detachments in Hilsea Barracks, vice Stevenson, appointed Adjutant to the 1st Royal Garrison Ballation.

— The London Gazette, Saturday 24 December 1803 source

Question

Why do we never get a first name for Stevenson?

The word “vice” is used here in the sense of “in place of” or “as a replacement for”. Ensign Barron is being appointed as the new adjutant at Hilsea Barracks, replacing Stevenson, who is moving to a similar position with the 1st Royal Garrison Battalion.