The other thread seems to have been talking mainly about the particular version that Lou Killen picked up, but it may have wandered off topic; I don't know if that was an arrangement of the set Bert Lloyd recorded at the Eel's Foot. I doubt if anyone seriously thought that the song originated in 1939: that is probably the earliest audio recording, though.

'Blackbird and Thrush' was a later form of the broadside song, though it seems to have introduced the 'pleasant and delightful' verse. Here is a list of those editions available at the Bodleian Library website:

The blackbird and thrush ("How pleasant and delightful is the bright summer's morn ...")

T & W Plant seem to have been contemporary with Such, though a J Plant was printing at the same address back as far as the early 1830s, I gather.

See also two earlier forms of the song, lacking the 'pleasant and delightful' verse:

The sailor and his truelove / Jemmy's farewell

For more detail, see

Marrow Bones (revised edition, 2007), 'The Soldier and His True-Love'.

I see that Dave has already added Steve's link, but here it is again for the sake of completeness:

Yorkshire Garland: Castle Hill Anthem