Lee Enfield No 4 Mk1 from an auction

[Potashminer]

OP - might want to find yourself a book like "Lee Enfield No.4 and No. 5 Rifles" by Charles Stratton. I have no clue what level of authority he is. Page 64 is a table showing a listing of the nine variations of rear sights that were used, according to him, by the 6 major manufacturers, for which years, of the No. 4 rifles. For example, as per that table, the "Mk.1" rear sight was used by Maltby during 1941 and 1942, then again from 1946 to 1955. Purely conjecture on my part, but if you considered how a rifle might be used in a serious close quarters fight, would expect that a rear sight assembly would be a part that had to get changed out fairly regularly?? So, I presume the armourers would have used whatever was "approved" and available, when they put the thing back fit for duty?
This all ignores that whatever parts might have been used by an owner at a kitchen table or basement workshop, after the rifle was sold out of service - likely 60 or more years ago?