Dax King mentioned an audio recording on YouTube of "A Real Slow Drag"
piano roll, stated to be played by Scott Joplin himself (MMD
17.05.14).

I believe that there has been only one piano roll issued of "A Real
Slow Drag" by Scott Joplin.  It was arranged by Ralph Mullins in the
1960s.  The roll was issued as original material on the PianoRecord
label along with other new arrangements of rags.  PianoRecord was run
by Lyle Martin in Pasadena, California.

Some of the PianoRecord material was reissued by Don Rand on the
Hollywood Vintage Series in the 1970s.  "A Real Slow Drag" was
originally issued on an unnumbered HVS roll (which I have), and later
reissued as Hollywood Vintage Series number 1100.

Perhaps someone has additional information.

Gary Watkins