@Steve Gardham: yes, the Opies and others have traced origins and development where they exist, but I was talking about the missing links between the 'Dark and Ancient' supposed original rhymes and the modern versions. I think the earliest printed version of 'Ring around a rosie' is from 1881 and we have a report of it being around as early as the late 1790s (though that's one claim, unsupported by any other sources) and no versions going back to the times of te actual black plague or bubonic plague - not even a literary mention of any such version.