larry beat me to the information referenced about dates, and docdrew did the honors with the very useful english proofs summary from diggory....the left side is the london proofhouse marks, and the right side are those of the birmingham house - your gun was proofed in b'ham, and as noted the original english proofs are those used 1896-1904 - so focus on those
on your 1st photo with the colored highlighting; the red marked symbols are the 2nd one shown (reading left to right), they are your basic proof, and are usually heavily stamped and so appear as a smudged mark.
and the green marked ones are the crossed halyards that are the 3rd & 4th symbols, one is the view mark and the other tells who did the inspection, and they are small enough to be hard to read.
the blue marks are exactly as you interpreted them.
the black marks tell that the barrels both had .008" constriction of choke - or MORE - they do not measure the choke, simply tell there is choke present.
on your 3rd photo with the colored highlighting; as matt notes, the tower is the scott's trademark - your gun is very close to the amalgamation of scott & webley in 1898, after which time there were some guns marked as scott's and some marked as webley's - i have a 1902 gun that is purely a webley, but has scott's name/address/and tower marks, along with the webley flying bullet marks - your yellow highlighted mark is not legible to me, but where it is located it is likely to be a patent reference....and i suspect it may regard the "improved scott's square bolt" top lock, which came into use around that time.
