Sorry all--this uneducated backwoodsman equated written as synonymous with composed.
Scott states--"this ballad, which is a very great favourite among the inhabitants of Etrick Forest, is universally believed to be founded in fact. I found it easy to collect a variety of copies; but very difficult indeed to select from them such a collated edition as might, in any degree, suit the taste of " these more light and giddy-paced times".
It has always been my view that the "plowboy" was intruded into the ballad at the end of the 19th C. with the advent of the bothy ballads.