It's pretty impressive for a razor made in 1867 which has 'seen a lot of use' to bear a stamp that only started showing up in 1891 and to have a perfect etch that goes over the top of blade pitting and the hone lines.
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Hmm, ok so wait..It was used by somebody who died in 1867, then by someone who died in 1911, and then after he died, a great grandson got it in 1909? Yeah, I'm a little confused. Anyhow, the razor looks authentic to me, disregarding the letter included, and assuming it's dated 1890-1900.