Unfortuantely, YouTube prohibits or has excluded classical music from YouTube Content ID. While this may perhaps be a little frustrating, there is sound reasoning behind it.
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Given the number of recordings of music from classical composers, it is essentially impossible for YouTube's system to accurately attribute the recordings to the correct artist. If two artist perform the same piece as it is written, the wavelengths will be nearly indistinguishable.

This is unfortunately a YouTube policy over which MusicHub has no influence. Self-composed classical pieces may be eligible for this in the future, but we cannot guarantee this. Thank you for your understanding.