Did the mark lack the second period/full stop as this one apparently does?
In the last photo on the barrel just below the Nock's Form, there is a crossed swords mark that looks like "AGP"; "Alfred G. Parker" ? There is a coincidental dent or scratch which I believe makes the "P" resemble a "B".
That is the Proof mark and year from the Birmingham proof house.
AB is 1950
The lower letter / number indicates the 'rank' of the viewer (examiner)
Mine are not the best, but they are not too bad. I can think of lots of Enfields I'd rather have but instead of constantly striving for more, sometimes it's good to be satisfied with what one has...