According to H.E.D. Hammond's notes in the Journal of the Folk Song Society (No 11- 1907 pp130-131), it was collected from Mrs Notley of Moreton in December 1906.
He writes - 'Mrs Notley had the song from a very old woman of Moreton, a famous local singer. The story of the song, she said, was that of a young man called to the wars in Flanders, went to pay a farewell visit to his love, whose father locked her in her chamber, thus frustrating the endevour. The title Flandyke Shore which Mrs Notley gave, is doubtless a corruption of 'Flanders Shore.'
To Hammond's note, Cecil Sharp has added:-
'I have a close variant of this ballad. The tune, which I noted down from an old lady in Somerton, is substantially the same as Mrs. Notley's, except that it is in 3/2 time throughout, and is in the Mixolydian mode. My version consists of four verses, the last two of which are more or less the same as the Dorset verses. The first two are as follows :-

When I was young and a courting did go
I loved a fair maid as my life,
From four in the morning till nine at night
I never would gain my heart's delight.

When her father came to hear
That I did court his daughter dear
He locked her up in a room so high
That was the beginning of all my misery.

As you say, the song as Nic sang it, is incomplete, so when the song appeared on the Albion Band's 'Acousticity' CD, it had a note by Ashley Hutchings:

'The much-loved Nic Jones found the traditional "Flandyke Shore" some years ago, about the same time as I discovered the song. He recorded it, I didn't. Recently, while driving through the Canadian Rockies in our touring van Chris (While) spontaneously started to sing the song which renewed our interest in, and love of the piece. She and I decided to give "Flandyke" a happy ending and by the time we had reached the United States border the task was completed.'

This is it:

So I hove a dart that touch-ed my true love's heart
Touch-ed my true love's heart
And brought the light into her eyes again.