To provide a parallel example, the score of a Mozart symphony has an inherent intelligibility to those who know how to read music, and especially to those who are trained classical musicians. To me, who has a minimal ability to read music, and no musical training whatsoever, it is just notes on a page. However, this does not mean that even my amateur ears cannot pick out a Mozart symphony when I hear it played--at least those pieces with which I am familiar.
The intelligibility, however, is not provided by the listener, nor even by the classically trained symphony. Mozart who was, of course, part of a musical tradition himself, provided the intelligibility, and the trained musician does his best to be faithful to the text. Should a new Mozart score be discovered, trained musicians could play it because of its inherent intelligibility.
None of this has anything to do with “private judgment.” Someone (either with or without the relevant musical skills), who just decides to wing it as he goes along rather than follow the score, is not “playing Mozart.” Someone with amateur skills, who does her best to follow the score, will nonetheless be playing Mozart, even if not with the adequacy of a classically trained musician.
In both cases, the inherent intelligibility is in the text. In the former, it is ignored. In the latter, it is revealed. The question of whether or not the musician correctly interprets the text is not provided either by the private musician, or even by the skilled guild of classical musicians. It is only because the text has an inherent intelligibility that skilled (or even unskilled) musicians can listen to a performance, and respond: “That is (or is not) Mozart.”
I'm not going to attempt to argue about Scripture, but Witt's claims about Mozart were perplexing. It comes down to what a musical score is, and what relationship it has to a musical performance. Is the score of a Mozart symphony the actual symphony, or instructions on how to perform the symphony? I would say the latter. I disagree that the intelligibility of a performance "is not provided by the listener, nor even by the classically trained symphony." Those are exactly who determine the quality of the performance, with most of the emphasis on the listener. Thus to some listeners a Mozart symphony has no intelligibility, just as to some listeners a Schoenberg symphony has no coherence.
As for the dividing line between the performance being "Mozart" or "not Mozart," I think it is much more nuanced than Mr. Witt makes it. I've heard improvisations that are very much in the style of Mozart. Since they are inspired by Mozart's compositions, do they not have some "Mozart" in them? I've also heard performances of Mozart's compositions that were not played in the style that Mozart envisioned, and therefore did not sound like Mozart. Are they still "Mozart?" I'd argue that both of these situations have some "Mozart" as long as the listener (me) still perceives Mozart's influence (his intelligibility?).