This is getting even messier. J. W. Ebsworth claimed in 'Roxburghe Ballads', VIII, p. 872, that the earliest copy known to him was a white letter issue in the Roxburghe collection, which he there reprints. (ZN1856 in the broadside ballad index on my website.) This is most likely an 18th century issue. Scott's version in 'Border Minstrelsy' is apparently derived from this. This is 25 verses long, and commences "My sweetest Sweet and fairest Fair". Later copies of this and two other versions are on the Bodley Ballads website. Search on 'Helen', then look at first lines.