Well, Bronson already commented that the field-collected versions of Child 4 that he numbered 73, 74, and 90 had absorbed the opening of "The Bailiff's Daughter of Islington," so the presence of this opening in a version of Child 4 does not imply any tampering on Pete Seeger's part. As Malcolm says, I suspect that the only part of "The False Knight on the Road" involved is the title; since "The Outlandish Knight" is sometimes called "The False Knight," "False Henry," "False Lover John," etc, this is not so outlandish either (pardon the pun).

Like Malcolm, I would expect the Nova Scotia set was Pete's primary source.