I can now see this information on McCormick several sites. Like Chinese whispers a viral piece with no source and no explanation of what the alleged earlier work is based on. If it is a derivation all fine, at least name they should name the source and alleged tune.
Otherwise I find it extraordinary that people keep having to come up with earlier derivations of works, and can't accept that songwriters come up with an original popular tune and lyrics, or sometimes both separately, without it being directly taken from an earlier source.   Someone has to have written a tune in the first place. If someone can name the alleged work fine, but otherwise these sites stating this about McCormick, are guilty of slurring the memory of a writer (though I don't actually like the words of 'Flower of Scotland', but you can't fault it for being an 'earworm' melody!)