The records of the British Brigade of Guards in America 1776-1781, mention both "lance corporals" and privates acting as corporals. For instance, the Grenadier Company Roster for March of 1779 (in "Orders, Returns, Morning Reports, and Accounts of British Troops" National Archives Microfilm M922) lists one lance corporal. Smith's "An Universal Military Dictionary" (London: J.Millan, 1779) on p.67 lists Lance-Corporal after the definition for Corporal. Lance-corporal = "one who acts as corporal."
Interestingly, Smith's dictionary does NOT mention lance-serjeants. I do have one scribbled note in my files on a corporal in the Guards being promoted to lance serjeant. Unfortunately, I can't find the documentation at the moment.
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