It appears that Andersson only noted one verse from John Sinclair of Flotta. He did, however, get Mr Sinclair's tune along with it; the earliest example (as Jack points out) that we have. The texts published with that tune have been taken from other, earlier sources. F W L Thomas didn't note any melody, but remarked that it was 'sung to a tune sufficiently melancholy to express the surprise and sorrow of the deluded mother of the Phocine babe'.

The website Sedayne indicates also has two further texts, given without any attribution.

The first is a slightly anglicized form of a text from North Ronaldsay, noted in 1860 by Charles R Thomson of Howar on behalf of John Keillor, the minister of the island. It has been quoted here recently, I think, in another thread. I imagine that the Orkney website compiler copied a transcription from the revival performer who recorded it, unaware that it contains modern alterations.

The second is taken from a text printed in The Orcadian for 11 January 1934, and that is the version given in Bronson II 564-5. It seems originally to derive from the text in R Menzies Fergusson's Rambling Sketches in the Far North and Orcadian Musings (London, 1883).

For a detailed study of extant versions of the song (from which most of the above information is taken), and a convincing dismissal of 'The Play o' de Lathie Odivere' as a late Victorian fabrication, see Alan Bruford, 'The Grey Selkie', in E B Lyle (ed), Ballad Studies (Folklore Society, 1976, 41-65 and 177-185). Bruford, incidentally, remarks 'A selkie is simply a seal, though readers of the ballad have tended to assume that in itself it means a seal which can take human form.'