Where did the version of Newry Highwayman in the DT come from?
With very minor changes and one verse missing it is the version from Colm O Lochlainn's 'More Irish Street Ballads' (if helpful, I could cite his notes on this song and his sources).
The missing verse is between verses 2 and 3 in the DT:
'Tis when my money it did grow low, Upon the highway I was forced to go; I robbed both Lords and Ladies bright And brought their gold home (2) to my heart's delight.
The Johnstons, BTW, sing exactly the O Lochlainn verses. On their LP they have the following 'exhaustive' note: They write the song is 'self-explanatory' and that's it.