Why are there omissions and discrepancies in Kaori's Kreutzer performance? In ep. 2, the entrants to the competition are shown playing extracts from the first movement of Beethoven's sonata no. 9 (often referred to as the Kreutzer). This is most likely the only movement played, given the portrayal of Kaori's performance and the length of the Kreutzer.

It would not be appropriate to show a performance of the entire movement. (It could bore viewers, and it could easily take up half the episode.) We can thus justify an abridgement of the piece or the removal of some of sections. The omissions I have found so far, however, do not make sense.


At the beginning, the section after the violin opening and before the statement of the theme (m. 5-18, mvt. 1) is omitted. The continuity of Kaori's movements might with the soundtrack imply that in-universe, she did not play those omitted bars, but it is unclear.
Later after the piano finishes its reiteration of the theme, there is a pause (which exists in the original score). Kaori then jumps to a later section (the adagio shortly after), which is merged with the ending of the first movement. It seems that this jump also occurred in-universe.
The "bland" part that the other violinists were shown playing, which should have fallen after adagio mentioned above, is skipped.


This leaves me with the following question. Is there any suggestion that the movement is actually being played with these omissions and discrepancies in-universe? If so, why would this be the case? Are these instead just badly executed (in that they are misleading) cuts? After all:


For the purposes of a performance used to assess musicians, certain omissions, particularly skipping repeats, could be acceptable. The sections involved do not fall into such a category.
Surely if all the violinists are playing the same set piece in the same competition, there should not be any obvious variation in what is played, even if some parts are removed for length.
The movement seems to be a reasonable length for a short performance, particularly if the one repeat that appears is taken out.
As requested, while this is not a conclusive answer, we might never know unless there is more information released.

The manga only specifies the piece, but never details the performances of the characters musically. The characters might gush over how "lively" or "beautiful" it sounds, but nobody ever talks in technical terms, much less describe sections of music.

Chapter 6 page 30-32 : The extent of description of Kaori's Performance.




Thus, we can conclude that your observations about the discrepancies in the musical pieces stem solely from the anime production. There could have been artistic/directional decisions for the eventual editing of the said pieces, such as time constraints or perhaps wanting to get a feeling across because that section or piece of music only fits that part. We might not know more unless more information is released (AFAIK) from the studio, such as interviews with the director/staff.

However, this stand does not exclude the author collaborating with the studio and affecting the said pieces. It could well be what the author had intended to portray in the first place. Again, we do not know the extent to which he has influence over the production, notwithstanding that the plot of the anime is pretty filial to the manga.

In my opinion, the "cuts" as you describe are not noticed by the general audience, and serve more as a mood setter and a plot driver than an actual portrayal of a performance. Only a more discerning and a informed listener would be able to tell that there was something amiss.