Well, here is my two cent's worth.  In addition to the works referred
to, I have a copy of John Edward Hasse's "Ragtime - Its History,
Composers, and Music" (Macmillan Press, London 1985).  This highly
readable book gives much useful detail about the musical form, and
its connection with the development of the player piano.  I can do
no better than to quote from it:

 "The phrase 'ragged-time' may well have its origins in 'ragged'
  (1886) and 'broken-time' (1888), and the phrases 'rag' and
  'rag-time' were first authenticated in 1896.  In 1897 at least
  _twenty-three_ rags (my stress marks) appeared for publication.
  Amongst them was Tom Turpin's 'Harlem Rag'.  Turpin was a good
  friend of Joplin, who's 'Original Rags', and 'Maple Leaf Rag' were
  submitted for publication in 1898."  I am not suggesting that
  Turpin was ragtime's originator, merely that there were plenty of
  others around at that time apart from Scott Joplin, who was in fact
  composing songs and marches in 1895 and 1896.  But when it comes to
  "Classic Ragtime", who could dispute that Joplin was the pioneer?

 "The arguments are clouded by time and perspective.  Even as
  far back as 1911, Juli Jones, a black theater critic opined that
  "The origin of ragtime and coon songs has taken up as much space as
  the race problem.  Every writer has a different view and backs it
  up with a good argument.  The Negro has figured in them all."

What therefore can we deduce?  I would suggest that a comparison
be drawn between John Field (the so-called inventor of the Nocturne)
and Frederic Chopin.  One gave an idea form, the other brought it to
a state of perfection.

If any further research is likely to prove productive, I would have
thought that the Chicago World Fair of 1893 should be a starting point.
There seems every likelihood that ragtime in some form or another was
played there.  Who were the main exponents, and what exactly did they
play?

Roger Waring