WAV, in reference to your insistence that traditional folk singers only sang the "top line melody" and did not make use of harmony or instrumental accompaniment when available.

pon•tif•i•cate   intransitive verb
Etymology:   Medieval Latin pontificatus, past participle of pontificare, from Latin pontific-, pontifex
Date:   1818
Definition 2:   to speak or express opinions in a pompous or dogmatic way.

Traditional singers often did sing together in harmony (ever hear field recordings of a group of women singing waulking songs?), and were known to use musical instruments to accompany songs if they had instruments and could play them. The harp has been associated with Gaelic song for at least 1,000 years and probably much longer. Otherwise, they sang without accompaniment—by default, not necessarily by choice. Because collectors may not have heard them do this does not mean that it wasn't done. The fact is that many collectors have heard this.

Don Firth