Eindridi, Hemingr,Toko, William Cloudesley, William Tell
What have all the above archers got in common? They all shot an arrow at an object placed on their son's heads. Is this diffusion of a story from Norway to Switzerland, or is it the operation of an archetype? I wonder why this story didn't get attached to Robin Hood? (Maybe because Maid Marian is a much later addition to the Robin Hood legends, and she would have been required for Robin to have had a son.)
This is something that occurs again and again with stories - you get a motif and it is repeated in slightly different forms across cultures. The story of Cinderella originated in China; the story of the faithful dog mistakenly slain by its master crops up all over the place (St Guinefort the holy greyhound in France; Gelert in Wales; and the story also appears in India). There is a Brothers Grimm story, The Queen Bee, that is essentially the same as a Siberian story, though the animal helpers are different.
I suppose you could have both diffusion and archetypes at work, in that the stories spread from one culture to the next, and because they resonate with people in an archetypal sort of way, they get spread further.
Discussion of diffusion in Popular Tales from the Norse by Sir George Webbe Dasent, 1904.
The Ballad of Adam Bell, Clym of the Clough, and William of Cloudesley