In the case of J. Seb. Bachs Orgel Fantasie und Fuge in g-moll—Für Pianoforte gesetzt von Franz v. Liszt
Liszt approached the work quite differently. He adds a number of dynamic marks, tempo directions, pedal directions and a certain amount of phrasing. This was possibly at the request of its dedicatee, Sigmund Lebert, the famous piano pedagogue, who may have feared that the average piano student would not know how to cope with a score unadorned by such indications. The piece was certainly published in the Lebert and Stark Piano School. In the revised edition (recorded here), at four places in the Fantasia Liszt suggests an alternative extra voice in place of rests, in no way intending to improve upon Bach, but attempting to recreate the grandeur of this most powerful work by reinforcing the texture.
from notes by Leslie Howard © 1991