The Volley sights etc were omitted from MkIII production & were not omitted to produce the pattern of rifle called the MkIII*
The LoC of 1916 is in 2 parts, part 1 is about changes to the future production of the MkIII & lists those changes, part 2 introduces the MkIII* which is the same as a MkIII but without a cutoff or slot & as such the changes to the MkIII were also applied.
I don't have the LOCs to hand and all my drawings and manufacturing / acceptance docs are in storage, but I will certainly look that info up for future reference.