Will post some photos next.
Dodson was established in 1867, but did not appear in the London directories up to 1870. By 1875, the first reference to Dodson in my London lists of Pianoforte makers is Wm.Dodson, 22A, Bryan Street, Caledonian Road, N.
He remained at Bryan Street into the 1920s, but seems to have finished in the 1930s.
Can you tell me what the wording immediately above the keys says?
The serial number is 6469, but although this is interesting to me, it doesn't help you with a date. The same number is pencilled onto the woodwork. Other numbers such as action and keys are not traceable.
It's very interesting that he experimented with 4 strings per note, as others had done much earlier, but the consensus is that they don't produce any useful effect. Do they sound very different to the trichords?
Email via my website.
If you find old references or links on this site to pianogen.org, they should refer to pianohistory.info