Hi, Bill -
I worked very hard to try to ensure that the lyrics of all traditional songs in the book are authentic, and Editor Peter Blood accepted almost all my recommendations on the traditional songs. I typed up a caveat for the introduction to the book. I posted it above, but here it is again:
Here's the instruction box I've submitted for inclusion in the songbook:

As is the nature of Ballads and Old Songs, there are many versions of almost every song in this chapter, and in many other chapters in this book. There is no "correct" version of any traditional song, and the versions used here are certainly not intended to be the "definitive versions. For the most part, they were chosen simply because they are reasonably authentic versions that work well for group singing. When you sing a ballad or any old song, remember that the most important thing is to tell the story well. Research the many versions of a song when you learn it and listen to a number of recordings, and feel free to substitute words and verses and even melodies that work best for you. Make your presentation of the song clear and interesting and lively. Do your best to memorize the lyrics, and don't be afraid to make up a line or a verse "on the fly" if you forget. Don't be a slave to any particular version of the song - sing what works best for you. And never, never tell another singer that he/she is singing the "wrong" version of a song.

And here's how it ended up, after editing:

There are many versions of almost every "traditional" song in this book. There is no "correct" version of any traditional song, and the variants included here are in no way intended to be "definitive." For the most part, they were chosen because they are reasonably authentic versions that work well for group singing. Try researching different versions of a song you're learning and listening to a number of different recordings, Please don't use our books to tell another singer that he or she is singing the "wrong" version of a song! Songs in the public domain are indicated in this book with "Arr.© 2015 Hal Leonard Corporation." under the song. The publisher has copyright to this particular arrangement, but you do not have to get permission to record or reprint lyrics to the song itself. For any other song you must contact the copyright owner of the song for permission to use it in any way.