 International Standard Music Number

Why was this so rarely used as of 2020s compared to ISBNs? It would have been perfect for helping find obscure records from Chinese traditional music and Indian classical music!

But instead we have Discogs, which is not too bad.

The International Standard Music Number (ISMN) is a unique identifier assigned to notated music, similar to how the International Standard Book Number (ISBN) is used for books. The ISMN system was developed to provide a way to identify and catalog music scores and notated music publications, facilitating their distribution and sales. An ISMN consists of 13 digits and is typically formatted as follows: "979-0-xxx-xxxxx-x".