Like a spiral, and like "doing philosophy,'' indexing never seems to end. But as Wittgenstein put it in On Certainty, explanations (34), giving grounds (110, 204), testing (164), justifications (192, 204), substantiations (563), and doubts (625) all come to an end, and so too much indexes: leave loop-holes open," he writes in On Certainty (139), "and the practice has to speak for itself" (Marjorie Clay, "A Conceptual Index of Wittgenstein's On Certainty," 1979).
She also published "Towards a Definitive Index of Wittgenstein's (Later) Work: More Terms for an Index of On Certainty" later in the same journal, but neither article actually contains an index. The titles made me hope someone had actually done it--something I've actually thought about doing. Most, if not all, W. books contain indexes now, but there are always things it would be good to add.