My long held theory as to why girls did not recognise their brothers before being seduced by them as in the "Bonny Hind" etc. relates to the fact that in Scotland up to at least the 17th.C. the eldest sons of some of the clan chiefs were fostered out at an early age, some of them not returning to their own clan until called back to take over as chief on the death of their father.
One such case in the mid 16th. C. was a Maclean from the Western Isles who was packed of as a babe in arms to his mothers people in North East Scotland who ever after on his return as chief of the clan was known in gaelic as the stranger.
Any comments? A previous airing of this theory did not even provoke a whisper from what is surely a large number of learned experts on ballad lore who read these forums.