Many thanks, Mr. Campin. I will PM you after posting here.

For what I can make out:

Although both sets of printed music in these sheets say
"A Lament for Nurse Cavell,"
to my sight-reading eyes it appears that these are two different tunes.
The pibroch, if that's what it is, is one tune, which when I try the A-mixolydian with its "two sharps," sounds much more effective than an A-minor reading as a non-wind-player would accept it at face value.

And the tune with two-handed keyboard chordal accompaniment, like a hymn, and two sets of lyrics, is a different tune than the pibroch.

Eneas Mackay published poetry by Murdoch Maclean, and may have published things by Malcolm MacFarlane although I can't confirm it. I suppose the whole Memorial to Edith Cavell thing was a situation for which the publisher made an exception.