Here’s the problem. Before the Pure Food & Drug Act of 1906, wines and spirits were almost unregulated, as long as you paid your taxes. With brands still in their youth, all an importer had to do was send a ship to Cadiz, buy a barrel of sherry, bring it home, and start pouring it into bottles. I see “dry sherry” advertised in American papers as early as 1774, and consistently thereafter, but I suspect what we’re dealing with here is usually an amontillado, which is fairly robust, being oxidized, and not a delicate fino. But then there’s John Q. Little, of Baltimore. This is from one of the ads for his saloon, from 1852:
That “Vino Fino” is pretty suggestive, and there’s manzanilla! At the same time, this is not something that one commonly sees. Again, barrel-ship-bottle; that means there was a lot of niche stuff that came into the country (mezcal, absinthe, vermouth, Fernet, old single malts, etc.), but very little of it was anything more than an attempt to see if it sticks or an accommodation for special tastes. None of the old recipes I’ve found for the Bamboo/Adonis specify what kind of sherry. Fino is possible, but the sherry you see advertised most is blended or oloroso or amontillado; the stuff that keeps and travels well. So I think the Consejo Regulador is right, but in the larger sense.
As for modern bartenders. In the oughts, Steve Olson and Andy Seymour did a whole lot of work teaching bartenders about sherry for the Consejo Regulador. One of the sexiest things to teach about was fino, because of the way it grows under flor and its delicacy and subtlety. It was a bridge to wine people, who thought the oxidized sherries were kind of old-fashioned and stodgy. NO residual sugar = elegant. So that plus dry vermouth = the most elegant way to make a Bamboo.
Personally, I prefer amontillado and Italian vermouth these days, but when I wrote Esquire Drinks in 2001 I went with “dry sherry” and French vermouth, and with Italian vermouth for the Adonis, included as a variation. In Imbibe (2007) I included Louis Eppinger’s recipe for the Bamboo, which actually specified French vermouth; “use a fino or an amontillado” was my advice). At the time, the Bamboo/Adonis was not well known. I had to teach it to a lot of bartenders when I ordered it. I would just say “vermouth and sherry 50-50” and see what they came up with if they didn’t ask for more detail. It came up fino an awful lot.