Robin, How you can equate the very old terms flash, swaddy and boondouk with "1905" is beyond me.

Flash girl is 18th century.

Swaddy appears in print in 1812 in a dictionary of Flash (OED); it is very old Br. military and cant slang. Swad also is an old (1754) and perhaps much earlier) cant word for soldier. In the 20th century, swaddy was gradually replaced in Army slang by squad(d)ie.

Boondook-boonduk is Hindustani, (nothing to do with the Boer War), and could have been picked up by British Troopers anytime during their more than three-century-long occupation of India.
(The American word boondocks, from the Tagalog of the Philippines, often confused with it and picked up during the Spanish-American War, ca. 1898-1902, means bush or back country (now widely used in Canada as well).

I am NOT saying that the "Trooper" version is old. The one in the DT wasa probably cobbled together by McColl for his album from several sources and has no useful significance as to age.