Volley and back sights on MLE and CLLE: why the difference?

[Sapper740]

I have an MLE and CLLE in my collection, both private purchase target rifles built by BSA at some unknown date. They both have the dial sight plate still attached, 1600 to 2800 yards. The dial sight plate on the MLE is stamped with the Roman numeral II, the CLLE's plate is stamped LES2. I was researching if the changeover from the Mark VI to the Mark VII round was denoted by other means when I chanced upon a little tidbit of information from Mr. Skennerton's book: the dial plates for CLLEs are graduated from 1700 to 2700 yards, not 1600 to 2800 as with the MLE. Further, the back sights also have different graduations between the two rifles: sight leaf marked to 1800 yards on the MLE, marked to 1900 on the CLLE. Was there a cogent reason for rifles with the same length barrels firing the same ammunition manufactured by the same manufacturer having differently graduated sights? Or is this simply another Lee Enfieldism?