I'm not familiar with "The Irish Rovers" (they'd be American, perhaps?) so I don't know which set of lyrics we're talking about; "The Girl with the Buckles on her Shoes" or "The Fairies" (as mentioned by "BigDaddy" above).  If the latter, then the point is that Allingham wrote his poem (as a poem, not as a song) a long time ago -it was first published in 1850, and it was never intended to be sung to the "King of the Fairies" setdance tune.  The version on the DT is garbled and incomplete, and evidently posted by somebody who copied it from a record (describing it as "Irish Traditional"; it's nothing of the kind!)  I've said before that if somebody actually has sung it to the dance tune, they must have used a very large shoehorn to force it to fit.  He didn't call it "The King of the Fairies", either, but "The Fairies".  Aarrgghh.  More fake tradition...

Rant over.

Malcolm