Re. 'Shule/Shool/Siúl/'Siúbhail' (and other spellings). Although fairly peripheral to the original question, the issue of 'correctness' does come up from time to time, and may as well be addressed now so that we all know what terms of reference we are using.

Admittedly more usually spelled 'Shule' (as in my post), you will nevertheless find the word rendered 'shool' in plenty of collections of songs from oral tradition if you explore the subject a little. As 'Shule Aroon', it appeared in songsters and on broadsides from the 19th century onwards; the later ones were chiefly American compilations on the lines of Six Hundred and Seventeen Irish Songs and Ballads [1898], but you'll also find it spelled that way in Irish publications; similarly with its relative 'Shule Agrah' (see Bodleian, Shule Agrah for a broadside by Haly of Cork which prints the interleaved refrain as 'Shule, Shule, Shule agrah' ... 'Gudhe tough, gudhe, tough, slaun'.

You won't find 'Siúl', which is modern 'Reformed Spelling', in pre-20th century examples; the older Irish spelling was Siúbhail, though it should be noted that non-standard forms were also common. 'Correctness' depends ultimately on context and usage, and here we are talking about a song widely circulated among people who didn't speak Gaelic themselves and -in the case of the majority of non-Irish singers- may never have heard that language spoken at all, so the refrain was rendered more-or-less phonetically, examples varying from reasonably close approximations to such as 'Ish come bibble ahly boo so real' (Arkansas) and 'Shall, shall, shally wiggle round' (Ozarks).

All this has been gone into in minute detail in previous discussions, and it would be redundant to repeat it all here. The most informative thread is probably Lyr Req: Suil a Ruin [1998-2008]: see in particular contributions from the late Bruce Olson. Read a little of those and you will see why I referred to the song as 'a special case' : it is an example of the relatively small category where what are now indisputably 'nonsense refrains' are demonstrably corrupted forms of phrases that originally made perfect sense. This is a small group. Attempts are frequently made (often based on the misapprehension that, because a few songs like this one can be explained, the same principles can be applied universally) to rationalise what are mere vocables as corruptions of all manner of things, but most of these, though frequently ingenious, are so anachronistic as to fall at the first fence.

Most of the contributions to this discussion so far seem to be repetitions of what has already been said in others, but I predicted that. It isn't surprising; there isn't much to say on the subject that would be new. My own comments above are also not new, of course. I make them only to clear up, so far as is possible, an issue raised which itself is not new (see, for example, Help: Suil A Ruin, correct spelling?, which also contains a range of dissenting opinions).