Richie,
Fascinating stuff! It doesn't surprise me that only one oral Lexington version derives from the broadside. This happens regularly this side of the pond with the older ballads. Where there have been several printings in the 18th century we get some versions of the ballad that derive from 19th century printings, but sometimes we get versions that derive from earlier printings of which the original is no longer extant. I accept it is more likely to happen your side of the pond as there have been large areas of land remote from printed sources and therefore oral versions can more easily develop without the interference of print.