Its a job to say, Tom. Like you said, Moss & Gamble Bros appear to be still trading. At any event, this pic showing the back of their works was taken in 1905 so they were still going then!
Attachment 127131
I found another Hawcroft razor on the net, this one has W Hawcroft and Sons Renown on one side and Concaved by F Koeller, Boston on the other:
Attachment 127132
Of course, that doesn't tell us much other than F Koeller, son of a Prussian immigrant and cited as a cutlery dealer age 43 in Bostom, Mass. along with his son Arther F. Koeller, 17 in the 1900 census. Arthur was in business - still trading as F Koeller & Son, from 99 Albatross Road, Boston, Mass and called a 'Razor Honer - Own Shop' in the 1920 census.
Attachment 127133 left: from 1922 Attachment 127134 left: from 1934
So F Koeller concaved that Hawcroft razor sometime before 1900 and probably sometime after 1880 or thereabouts, when he would have been 20. Which, as I say, does not give us the age of the razor, just a pleasant diversion!
Regards,
Neil