Bruce, I wonder if we can't use somewhat more precise language than "facts" and "speculation", or at least less loaded terms. There ought not be any doubt that it is a "fact" that folk-tales incorporate generic elements -- motifs -- that link them to a specific tradition within the greater genre. It is, for example, a "fact" that stories about King Arthur, Charlemagne, Tsar Alexander I, and Nero all employ two related motifs: 1. the culture hero or divinity who has not died but is still alive and 2. the culture hero or divinity who is expected to return at the proper time (Thompson, 1953, motifs A570 and A580). It is an act of interpretation (the connotations of which I prefer to "speculation") to say that these motifs transcend (a bad word) the particular story in which they are present to establish a relationship with other stories of the same typology. I don't see why it is not also interpretation (or, if you prefer, "speculation") to determine which songs of a collection are forged.
I am trying to find a fundamental difference between my speculation and other, more legitimate kinds of interpretation. The only distinction I can come up with is that the units/objects of analysis are, in my case, more abstract than in other cases. But -- I plead with you! -- heuristical tools like the notion of "genre" reflect reality. These terms I am throwing around exist in the real world. We ought to recognize their import and incorporate considerations of them into how we talk about the music. What I do with them in particular is another matter -- that's where my interpretation might be flawed.
I apologize if I am being overbearing (and it is awful if I am being rude -- I confess ignorance of forum etiquette), but this is one my most desperately ground axes. There is so much to learn about the music if we can think about it in these terms. Alan Dundes, someone I've seen you cite in the past, is a proponent of the "symbolic" reading of such tales as these, and it seems to me that he provides very satisfying (and believable) readings that profoundly deepen our understandings of the tales by placing them in a cultural (read:symbolic) context.
But, on a lighter note: Art, I very much enjoyed your reading of "John Henry". It shows what we can do without resorting to the sort of sorcery I tend to employ. (Although, I am afraid that I cannot allow either that you have left the drawbridge of speculation for the castle of facts.) And, Barry, I am 100 pages into "The Land Where the Blues Began." Thank you, and consider your good deed for the day accomplished.