Is the version in the Digital Tradition an accurate rendition of the "shorter" version of the song? Yes. In verse 2, the usual is " their DUTY to fulfill" - you'll know why! The last line of that verse has a few versions, also.
Who has recorded that version?
Don't remember. A quick check shows a few recordings around 1973 - but I know there were several before that. Paddy Reilly? Not sure.
Is it agreed that we should add an attribution to Michael Considine as songwriter?
Don't see why not.
Are we convinced about the accuracy of the "longer" version that Frank posted - did he transcribe it from McMahon's cassette, or what?
See Alice above. Verse structure and content are fine - the odd word gets changed in individual performance.
Can somebody find out how Frank McGrath obtained the information from McMahon?
He asked! Regards
p.s. In verse 3 of Christy's version, he uses the second part of verse 5 of Robbie's.