Noilly Prat Ambré, the vermouth many favour for this cocktail, was first made in 1986. As reproduced above, the original 1884 recipe merely calls for "French vermouth."
Thanks for the clarification. I was under the impression that the goal for this recipe was to keep it "authentic" to the period/timeline, so far as we know it.
I really do appreciate the direction that you're taking this site, Simon! Thank you.