RJW,
Lithgowproduced MkIII*s with cutoff slot in the early part of 1918 when production switched to the MkIII* a good indicator of a 1918 being one of these early MkIII*s is the * being stamped within the shield, most of these rifles show up with the * barred out, mine included, mine also came to me without a cutoff but i have chosen to leave it as it is.
Only the presence of a cutoff denotes whether a rifle is a MkIII or not, windage rearsights were fitted to early MkIII*s as well.