I'm planning to self-publish some of my scores, and will probably also be publishing some scores for friends and colleagues. I'm confused as to whether my publications should have ISBNs or ISMNs.
Bowker (who issue ISBNs in the US) are quite unequivocal on their website:
No, sheet music does not get ISBNs. The ISMN is the appropriate standard for sheet music, which doesn’t have any binding. ISBNs are not assigned to books of printed music.
Nielsen here in the UK seem to agree:
Some examples of products that do not qualify for ISBN:
However, when I look on my shelves (or rather the piles on top of my piano) I find that most of my books of commercially published sheet music do have ISBNs, even when they have no end matters or musicological commentary and are just the scores and a contents page. The only one I can find with an ISMN on it also has an ISBN right next to it.
Clearly practice is at odds with theory, so what should I do? I'm not expecting to sell more than a handful of copies, but do want people to be able to find my scores on Amazon etc. so they will need an identifier of some sort. ISMNs are significantly cheaper than ISBNs so that may be the deciding factor if all else is equal.