The chamber length (2 1/2"), shot charge (1 1/8 oz.) and 12 over C in the diamond are 1925-1954.
1925 - 1954 the 2 1/2 & 2 5/8 12g maximum service load was reduced to 3 Dr. Eq. with 1 1/8 oz. shot with a mean pressure of 3 1/4 tons by LUP = 9,800 psi by Burrards conversion.
According to a post on shotgunworld by user RPRNY, In 1896 the firm moved to 165 Piccadilly and in 1902 to 8 Craven Street, Strand.
In 1908 Cogswell & Harrison took over the firm, and Robert yGrey joined them. This was probably when the Aldershot branch closed.
In 1917 Cogswell & Harrison moved the company to their own premises at 226 Strand and William Moore & Grey ceased to trade under their own name.
I could swear that the above info had also been posted on this forum, but I couldnt find it just now.
Thats what lead me to the 1917 date at the latest, given the Craven St. address on rib.