Roud 12 is called "The Elfin Knight." You would definitely know it better as "Scarborough Fair." It's about a magical man and his would-be young bride. And it's about an old merchant's fair in North Yorkshire. And it's about 4 herbs, which you know very well. 

There's a lot of modern history with this song, so as such, there's a LOT of information. 

http://everyfolksong.xyz

http://www.scarboroughsmaritimeheritage.org.uk/