Though the primary purpose of the NLE is still the publication of the final version of each work, earlier versions of many of the works which differ significantly from the final version have been included in the appendices to the volumes, especially in the second series.
The NLE Supplement volumes, which have been published since 2005, are the successors of those appendices; in making available the earlier versions, their function is to enable the reader to look into Liszt's compositional process and to provide an opportunity for pianists and musicologists alike to better acquaint themselves with Liszt as an artist. Publication of the Supplement volumes is also justified and supported by the quantitatively and qualitatively significant achievements within Liszt philology during recent decades. These findings are, as always, fully taken into account and utilized by the NLE editors in preparing the Supplement volumes for publication.
The main aim of the editors (Adrienne Kaczmarczyk and Imre Mező) in compiling the Supplement volumes has been to make the earlier versions of every solo piano work published by the composer or others accessible. In addition, they have included in them complete, fully worked-out compositions and earlier versions surviving in manuscript form which are of indubitable musical value and thus may find a place in the concert repertoire.