"
Flash. This word already had several meanings when "A Dictionary of Buckish Slang, University Wit and Pickpocket Eloquence" was published in 1811. Much of this was published in the 1754 "The Scoundrels Dictionary, or, an Explanation of the Cant Words used by Thieves, .... .... "and a Collection of Their Flash Songs, with a Proper Glossary" (not seen).
From the 1811 edition-
"

Haven't yet chased this, but "the flash girls of the city" seems, as a term, to be local to "The Trooper ..". Coming in about 1905.

The girls are generic -- starts with the gallows-whores in the Irish 1790 fragment, and jumps to the (believe this!) "maidens" of the American Laredo.

But flash girls collocates with squaddie and boondook in "The Trooper .." As far as i know, the term doesn't occur elsewhere in the versions.

So ... unless I'm totally off the wall (which is all too possible) the flash girls contemplating the corpse of the clapped out trooper locate this version in 1905 -- squaddie/boondook/flash girls.

The slang dictionaries I've consulted (OK, Partridge) lock all three terms around a blurred 19thC. Big deal.

{Ah, have we yet raised the interesting segue of the Dead Buck from officer class [whether regular, militia, or marines] to Other Ranks, when he becomes a squaddie?

:-(   }

Robin