It is well possible as you have pointed out & can't confirm any of this either way.I have a small collection of Sports 11 or so & the only things that are definite as to models are the rear sight difference between cals,butt pad, the MKII stamping all of these have the metal trigger ,the safety differs also but is same on a couple of early ones but these could have been changed.The checkering changes then reverts back to MKI style in between the years some where & some of what i believe are MKI's have metal triggers again could have been changed later.
Then to complicate it more the 124 i have looks to be a MKII numbers start with 42 does NOT say MKII on breach & has the interchangeable elements so as you see hard to define.
Just put on which ever you like no one will mind.