What's interesting about the fact that history often gets distorted in "popular" media such as folk music, it also gets pretty wacky in the hands of the "official chroniclers" as well.

Certainly at least until the Reformation, much history was recorded for posterity by clerics, who had their own particular reasons for portraying events and personalities in a particular light (William Rufus in the 11th century comes especially to mind--no great patron of the Church and an essentially irreligious man by the standards of his day, his portrait was pretty unflattering as painted by contemporary chroniclers; ditto King John in the less-than-objective journalistic hands of Matthew Paris 100 years later!).

The other major faction of chroniclers tended to be literate Court writers (also with clerical backgrounds; "lay" clergyman) like the brilliant Jean Froissart, who wrote for posterity but also for personal advancement, and even literary geniuses like Chaucer and Boccaccio, writing fiction and verse that paints a vivid picture of their impressions of their times. In any case, how much of the actual facts of any given situation are represented is really anybody's guess. I'd guess that the versions of events recorded in folk music are probably as accurate a reflection of the popular view of events as the chronicles are of the viewpoint of the more literate elements of society.