There are several recommended identifier types that specifically apply
to music, but I don't know how to tell them apart. These are "music
publisher," "matrix number," and "issue number." Is there any way to
tell, just looking at a code printed on a disc/sleeve/jewel case insert,
what the type attribute should be? The examples for field 028 on the
LoC site don't clarify things for me.
Also, does anyone know of a reference (online or print) for
obsolete/historical publication or product codes? Sometimes I come
across identifiers on older books (e.g. "0076-668-6016" on a Japanese
publication from 1978), and I don't know whether they derive from some
disused national or local standard, which I could use as the type
attribute, or from the publisher, for which I'd use "stock number" as
the type attribute.