And don't forget, royalties are payable to the copyright owners of the lyrics/songs/tunes as well as the performers.

This is a REAL minefield, especially bearing in mind the well-known story of the people who went around claiming copyright of existing traditional songs. One famous example is Wild Mountain Thyme, which is clearly based on Robert Tannahill's Braes o' Balquidder from the 1790's - see below. There is nothing to stop anyone doing that even now.

It would be really difficult to find a single album of "traditional" music where all songs/tunes are public domain. So we can assume that royalties are being avoided if none are paid.

From Braes o' Balquidder:
I will twine thee a bower
By the clear siller fountain,
An' I'll cover it o'er
Wi' the flowers o' the mountain;

Will ye go, lassie, go,
To the braes o' Balquhidder?
Where the blaeberries grow,
'Mang the bonnie bloomin' heather;