For the Edgar Coyle song
Discogs has
A Letter From Mary Of Mourne (Mary's Reply To "Mountains Of Mourne")
"1920s repress of Nov. 1912 release"
www.discogs.com/release/16040739-Edgar-Coyle-The-Mountains-Of-Mourne-A-Letter-From-Mary-Of-Mourne
&
www.discogs.com/release/15400760-Edgar-Coyle-The-Mountains-Of-Mourne-A-Letter-From-Mary-Of-Mourne
Columbia – 2009 R
and credits the words to David Buchan*
sung by Edgar Coyle
released 1926

DAHR has two pages
Release Date: 11/1912
https://adp.library.ucsb.edu/index.php/objects/detail/474081/Columbia_U.K._2009
&
"Take Date and Place        approximately 1923 London"
https://adp.library.ucsb.edu/index.php/matrix/detail/2000103891/73376-A_letter_from_Mary_of_Mourne



*note Discogs has only one song by 'David Buchan'.
There was also a folklorist with the name David Buchan (1939 – 1994)
www.store.abdn.ac.uk/product-catalogue/publications/the-elphinstone-institute/the-ballad-and-the-folklorist-david-buchans-collected-papers