I am responding to Mike Knudsen's questions about: (1) whether Joplin
added the improvisational bass figures on his "hand played" rolls, and
(2) whether such improvisation is proper.

Mike, I recently responded to some inquiries about my "company's" piano
rolls (Meliora Music Rolls) where your second query came up.  The
customer questioned whether my adding very slight ornamentations was
proper; my reply to him responded to both of your questions:

  "I understand what you're saying about my deviation from the sheet
   music, but my real worry was that I didn't do enough improvisation. 
   ... As you may know, ragtime performers deviated extensively from 
   the music during performance.*"

* Sources: Rudy Blesh & Harriet Janis: "They All Played Ragtime" ; 
and Jasen & Tichenor: "Rags and Ragtime - A Musical History" (New
York 1978).  On page 6 of Jasen & Tichenor it is stated: 

  "Only the mediocre ragtime performer, who lacked the capacity to
   create his own individual flourishes, was limited by ragtime sheet
   music.  Even Joplin, who took a strict view of ragtime as an
   unalterable written form, was willing to add bass embellishments to
   the seven rags he produced as piano rolls. ... 

   [footnote in original text]: All piano rolls which were "hand-
   played" are open to question as accurate and faithful records of a
   performance.  Unlike phonograph recordings, notes could be added or
   subtracted to a master roll after the initial performance.  However,
   in 1959 [two Joplin rolls were played for] Arthur Marshall, Joplin's
   close friend and fellow ragtimer from the Sedalia and early St.
   Louis days.  When his attention was called to the quick octave
   embellishments in the bass, Marshall responded: "That was his
   style.""

I hope this helps.  I think its fascinating to have a confirmation 
of these facts from someone who collaborated with Joplin and actually
heard him play.

Tim Baxter