The two extra verses there Chris made up himself, though they're composed mostly of elements from other songs re-combined. Whether they really add much is hard to say; they seem rather odd and uncomfortable to me, but they might be helpful for listeners who aren't very familiar with the traditional form of the song. It's worth mentioning that, though it's often been observed that the narrative seems incomplete, it appeared in that form on broadsides too and was immensely popular in its day, so clearly our 19th century ancestors had no trouble with it as it stood.