Ewan, I've been puzzling over ther relationships between all the related songs on my website for over 30 years. There's barely enough of "I know where I'm going" to identify it with all the others. There are roughly three distinct tunes for all the songs with overlapping verses. Fragments of the song are in Herd's MSS but the earliest tune is that for "Jess Macpharlane", that appeared just before "Ay waukin, Oh" was published in 'The Scots Musical Museum'. C. K. Sharpe said Jess MacPharlane was a celebrated Edinburgh beauty of the 1740s, but I've never seen any note of the song so early (and I looked hard). If he's correct that may have spawned the other songs. (I contributed the song to 'Folk Music Journal' 1968, in response to an earlier note, 1966, that the "Licht Bob' Honey" (Greig collection) was to the same tune as "Ay waukin, Oh". [I have the 7 vols. of Grieg-Duncan, and have vol. 8 on order.]

I just don't know if there was some early ballad, 1750 or earlier, that later songs borrowed from, or whether just a few verses at a time were borrowed for one song from another. Do look at all on my website, were I've given many and noted others.