Partly from an interview given to Fiona Richie (host of the Thistle & Shamrock radio program) a few years back. I don't remember the name of the scholar who was discussing Jacobite songs with Fiona, but this background was given in the interview. I'm rather familiar with the period from my research on the political history, but not so much with the folk songs of the era. I know many Jacobite songs were written later during the decline of Jacobitism (late 18th-early 19th century) and, as you mentioned in an earlier post, openly mention Bonnie Prince Charlie, etc. There are, though, many songs (Ma Plaid I belive to be one of them) that were either derived from an earlier source, or were simply written with the coded references to begin with. If I can find a transcript of the interview with Fiona Richie, I'll post it.