SpikeDD, the MkIII did not turn into the MkIII* it is a stand alone model.
The LoC of 1916 is in 2 parts, the first part lists modifications to the future manufacter of the MkIII not what defines a MkIII*
Part 2 introduces the MkIII* which may embody modifications listed in part 1
The only difference between a MkIII & a MkIII* is the cutoff slot.
What configuration the early MkIII*s came out in is a bit of an unknown but from the LoC the only difference may have been the cutoff slot as the LoC clearly states the MkIII* may embody modifications listed in part 1 so they could have any of the early features, if not all.
Ironcally what i believe from references i have read the original MkIII* pattern was to be what we know as a post 1916 MkIII with a cutoff.