In answer to your first query the likelihood is that the oral versions derive from another printed version, perhaps now lost, that omits this stanza. I'll have a look when I get more free time. The Santa Barbra site probably has most of the early printed versions.

The second query would need checking carefully to see in which versions it occurs before making any guesses as to where it came from. Again I'll have a look. Off the top of my head if an equivalent stanza occurs later in the ballad in printed versions it is not beyond the skills of the singers to interpolate the later stanza into a new stanza that helps the story along in an earlier part of the ballad. Peter Buchan was an expert at this.