I've pondered the same thing, lancaster. My opinion, for what it is worth, is nadda/no sight regulation beyond point blank range out to 150yards - MAYBE.
Where would this testing/filing/testing be done by a London or Birmingham maker, for the ranges noted by the sight leaves?
Due to his experience, when putting sights on rifles he makes, my bro usually has all his rifles put the first ball within 2" of the bull at 25yards.
I am sure these cape gun and DR makers are/were certainly capable of the same.