Young Buchan - Hares/Sally not particularly E Anglian, but widespread: Sedley's HotM in Seeds of Love, e.g., collected by Hammond in Dorset, collated with a Williams 'Upper Thames' version, tune from another Hammond/Dorset version.

Not happy about your 'easily': it certainly has happened: to say that it will 'easily' happen, so long as there is a similarity of format while no connection in theme appears to me to beg the question. We know that; but it doesn't add to the understanding of why it has happened so regularly between these two.