Charles R. Martin, "Adventures of a Highland Soldier on Active Service
at Home and Abroad" (Ottawa, 1892), p.5:
"We arrived in Cork at about six a.m. of a Sunday morning [in January, 1868]., and as we marched through the streets with the band playing 'Scotland the Brave,' you could plainly hear them say, 'What a foine body o' men,' etc."
Martin enlisted in the 92nd Gordon Highlanders in 1867. After nearly twenty-five years, his memory may have been incorrect, but at least he firmly places "Scotland the Brave" in the latter 1860s as a favorite march; this is in line with the contemporary mention of it in the Morning Post as being played in London in 1869.
The plausible appearance of "Scotland the Brave" in Ireland in the late '60s supports the idea that Corrigan's "Irishman's Toast" became known to uillean pipers not long after, though perhaps they did not know (or appreciate) the Scottish military title. Hence its replacement by "The Irishman's Toast" and possibly others - including, apparently, "O'Donnell Abu."
A number of Scottish tune books for war pipes were published in the nineteenth century. Few of these are online. It now seems likely that "Scotland the Brave," under one title or another, appeared in one or more of them even before the Gesto Collection in 1893.