Enforcers tips please

[PrinzEugen]

Thanks very much for that fulsome answer! The trouble with looking at a few is that they tend to be at opposite ends of the country.
So the bipod was by no means standard fitting then - I kind of assumed it was? What range of scopes are known to have been fitted and does whether they are numbered depend on the date of manufacture (eg early ones) or is it entirely random?