My previous reply was in response to MBSGeorge who said that this had not been answered.
In response to your assersion that this was drafted in for the sake of rhyme I would say that when discusing the development of folk songs through history anything is possible, but there are things that can be said for certain.
The storyline of the ballad closely resembles A Gypsy Laddie which is given as a tradition of Renfrewshire in 1825 although it was in use much earlier than the date of the written reference. Renfrewshire being the geographic location of the mouth of the river Clyde, I find the reference to the river Claydee more compelling. The ballad minus the ah-de-doo-dah chorus,and with no reference at all to a specific river harks back to a much earlier date when gypsies were outlawed in Scotland, and indeed some were hanged. The tradition of handing songs down by word of mouth among people who could not read or write has no doubt lead to this particular song being re-written many many times. Still, it provides for interesting, if rather fruitless speculation.
I have nothing but admiration for Leo Maguire who made himself some easy money in the days before hordes of copyright lawyers could decend on him. Incidentally what is the collective noun for copyright lawyers, I suggest 'A Shyste'.