So taking from what Bruce is saying the mag cut off was deleted as of Jan '16 I have a 1916 Lithgowicon MkIII* that has the mag cut off fitted to it I also know from I think it was either yourself Bruce or another member that the rifle had a barrel change '37 barrel replacement to "H" thus stamped on top of the butt wrist (Still do not know why) could the mag cut off have been fitted then.
Does that mean that subsequent receivers made after the Jan '16 date were not to have the cut out slot and screw hole machined into it. TIA