> The ur-ballad has branched off from its Norse roots and taken different forms with a variety of refrains.

It is a striking feature of this ballad just how different these forms and refrains are. AFAIK no other ballad comes close to having such a variety of forms. Several persons must have quite deliberately rebuilt this ballad at one time or another while keeping the same plot apart from the inclusion or exclusion of the resuscitation stanzas, either working from previous versions in English or perhaps making new translations from Scandinavian versions.

A few days ago I commented that Brian Miller's version was the first I have ever met where the dead girl's ghost instructs the musician to use parts of her body for his instrument, and where the elder sister's punishment is tit for tat: to be drowned. I am now reminded that this is Child O apart from the omission of a few verses and some other very minor changes.