This is from Dig's chart that you linked
The Supplementary Nitro Proof Revision of 1904 is here from
The Gun and Its Development, 1907
http://books.google.com/books?id=3HMCAAAAYAAJ&pg=PA280p. 291 mentions the 1896 Rules "Maximum" mark, and p. 292 shows the MAXm. powder grains and shot mark. I don't know when that was discontinued and only the "oz. Shot mark" was stamped.
https://www.vintageguns.co.uk/magazine/rules-of-proof-5-london- This is an 1896 Lancaster marked “E.C.” (No. 1) 42 grains = 3 Dram with MAXm. SHOT 1 1/8 oz.
A Tolley 1896-1904 1 1/4 oz MAXm but not the grains
1904-1925 London Proof - no oz. SHOT
https://www.vintageguns.co.uk/magazine/rules-of-proof-6-london-1904-1925 Birmingham reproof - no oz. SHOT
https://www.vintageguns.co.uk/magazine/rules-of-proof-8-re-proof-