Colli and Montinari research

While researching materials for the Italian translation of Nietzsche's complete works in the 1960s, philologists Giorgio Colli and Mazzino Montinari decided to go to the Archives in Leipzig to work with the original documents. From their work emerged the first complete and chronological edition of Nietzsche's writings, including the posthumous fragments from which Förster-Nietzsche had assembled The Will To Power. The complete works comprise 5,000 pages, compared to the 3,500 pages of the Großoktavausgabe. In 1964, during the International Colloquium on Nietzsche in Paris, Colli and Montinari met Karl Löwith, who would put them in contact with Heinz Wenzel, editor for Walter de Gruyter's publishing house. Heinz Wenzel would buy the rights of the complete works of Colli and Montinari (33 volumes in German) after the French Gallimard edition and the Italian Adelphi editions.
Before Colli and Montinari's philological work, the previous editions led readers to believe that Nietzsche had organized all his work toward a final structured opus called The Will to Power. In fact, if Nietzsche did consider producing such a book, he had abandoned such plans in the months before his collapse. The title of The Will to Power, which appears for the first time at the end of the summer of 1885, was replaced by another plan at the end of August 1888. This new plan was titled "Attempt at a revaluation of all values" [Versuch einer Umwerthung aller Werthe], and ordered the multiple fragments in a completely different way than the one chosen by Elisabeth Förster-Nietzsche.
Mazzino Montinari and Giorgio Colli have called The Will to Power a "historic forgery" artificially assembled by Nietzsche's sister and Peter Gast. Although Nietzsche had in 1886 announced (at the end of On the Genealogy of Morals) a new work with the title, The Will to Power: An Attempt at a Revaluation of All Values, the project under this title was set aside and some of its draft materials used to compose The Twilight of the Idols and The Antichrist (both written in 1888); the latter was for a time represented as the first part of a new four-part magnum opus, which inherited the subtitle Revaluation of All Values from the earlier project as its new title. Although Elisabeth Förster called The Will to Power Nietzsche's unedited magnum opus, in light of Nietzsche's collapse, his intentions for the material he had not by that time put to use in The Twilight of the Idols and The Antichrist are simply unknowable. So The Will to Power was not a text completed by Nietzsche, but rather an anthology of selections from his notebooks misrepresented as if it were something more. Nevertheless, the concept remains, and has, since the reading of Karl Löwith, been identified as a key component of Nietzsche's philosophy, so much so that Heidegger, under Löwith's influence, considered it to form, with the thought of the eternal recurrence, the basis of his thought.
In fact, according to Montinari, not only did the Will To Power impose its own order on the fragments, but many individual fragments were themselves cut up or stitched together in ways not made clear to the reader. Gilles Deleuze himself saluted Montinari's work declaring:
As long as it was not possible for the most serious researcher to accede to the whole of Nietzsche's manuscripts, we knew only in a loose way that the Will to Power did not exist as such (...) We wish only now that the new dawn brought on by this previously unpublished work will be the sign of a return to Nietzsche.

Drawing on this research for support, Montinari also called into question the very conception of a Nietzschean magnum opus, given his style of writing and thinking.