Why is it difficult to reconstruct lost gagaku solo music?

Reconstructing lost solo music for gagaku instruments is difficult primarily due to the nature of historical musical notation and the reliance on oral tradition.1

Historical gagaku notations were not comprehensive scores but rather served as mnemonic memory aids, functioning similarly to Western "lead sheets". These part books provided only a skeletal framework of the music, such as single notes for multiple beats or names of stereotyped patterns, rather than detailed guides to the performance.21

Because the notation lacks the specific nuances, subtle ornamentations, and full melodic content of the pieces, the music was designed to be learned through rote methods under the direct guidance of a teacher. Players used shoga—a system of singing syllables—to memorize instrumental parts, which further emphasizes that the complete musical experience was intended to be transmitted orally. Consequently, because these essential performance details were never fully documented, the loss of the oral tradition makes it nearly impossible to accurately reconstruct lost solo repertoires or fully evaluate the performance practices of the past.12