More sole survivors

I recently wrote about Randolph Murray's return to Edinburgh with the Blue Blanket after Flodden, the sole survivor of the City Band. There is, of course, a rather more famous sole survivor of Flodden associated with Selkirk. This individual is said to have returned to the town carrying with him a captured English banner which he cast down silently before the townsfolk. He then either collapsed from exhaustion or expired immediately, depending on which version of the story you happen to be reading. This event is marked every year in Selkirk as part of the Borders Commons Riding season. The banner itself survives to this day in Halliwell's House Museum in Selkirk, and is an English banner of the correct vintage, now known as the Macclesfield Banner
But what was this solitary rider's name? There is a statue outside the Victoria Halls in Selkirk, erected in 1913 to mark the 400th anniversary of the battle, known as the Fletcher monument (above), following a local tradition that his name was Fletcher. Walter Elliot, that tireless collector of Borders lore, has remarked that there are no contemporary records of a sole survivor of whatever name returning to Selkirk with the banner nor was anyone of that surname mentioned as living in or near the town in the period.
A different tradition records that the sole survivor was the town clerk Sir William Brydon,fletcher by trade, who had led the men of Selkirk at Flodden and who was knighted by James V in 1535 for his actions there. Sadly, this also appears to be untrue. Brydon does appear in contemporary documents and was indeed the town clerk in 1513, but in not mentioned as having a Flodden connection. Some documents do indeed style him "Sir William Brydon", but not as "Sir William Brydon, knight", which means that he was a priest of some sort.
It's not impossible that he fought at Flodden–other priests certainly did, and there is still a sword extant that is said to have belonged to him–but there's no contemporary record of this either. So, perhaps the truths of the sole survivor story are artistic rather than historical.
This is a shame, because otherwise it would be a nice piece of synchronicity. There is another very well-documented case of a sole survivor of a disastrous military expedition, a Scottish surgeon who arrived at Jalalabad on the 13th of January 1842 to report the total destruction of the army commanded by General Elphinstone during the famous Retreat from Kabul, part of the First Afghan War. And the name of this man, commemorated in Lady Butler's Remnants of an Army (below)?
It was William Brydon.

[pictures from Wikipedia Commons]