Hi Ray! Actually, i believe that style of hand guard seems to have come out in 1919. Two original Mark I rifles I've seen with 1-19 barrels (mine is one of them) still have the High Hump hand guard. So the change over seems to have occurred after that.
I believe my 1920 National Match rifle with a 11-19 barrel date is all original. Maybe Rick Slater or John Beard could verify or negate that.