@hue-man,
Puccini died in the midst of Turandot, and someone else finished it for him based on a some sketches and discussion. Heidegger, in his discussions of Nietzsche, often prefers to use his unpublished notes rather that what N. felt worthy and important to publish.
"Completing" an unfinished philosophy, or an unfinished life, seems always a matter of interpretation, and one must judge whether the attempt is an honest and earnest one or not. Nietzsche's thought is always in transition even in his published works; as the philosopher of becoming this is perhaps fitting and proper. Consider how the Dionysian in BT becomes transformed into "Dionysus vs. the Crucified," or the unfinished portrait of the Overman. Consider that while there may be a general agreement amongst subsequent philosophers and scholars about the important themes in N's work, there is much less consensus about what he actually meant and the ranking of even those themes.
So perhaps saying that Reginster offers an interpretation is not necessarily a con in Nietzsche's case.