Perhaps true, but Chopin and Liszt wrote in a very improvised way. Especially Liszt. This "improvisational spirit" can be a certain rubato, but only a hint. This line of though is very deep and I simply cannot explain it easilly. Few seem to understand it. Perhaps Professor Joseph Stanford (piano) will understand.
I am sorry. Mozart could change, but I am not a big fan of that. Forgive me. This is so difficult.
Let me put it again:
With improvisational spirit it is interpreting the way Paganini would have interperated it. Like hearing different versions of his Vioin Concerto's, as is the same with an improvisational spirit. If anyone understand what I am trying to get to, let me know.
