They need to use:
Code:
<dc:identifier id="id">URN:http://www.gutenberg.org/74324</dc:identifier>
or if they don't want to do that, they they need to create a refines that sets the scheme to URN. Although I would not recommend that, as nothing supports it and the geniuses that created the epub3 spec got their own examples using it wrong in the initial version of the spec.
https://idpf.org/epub/301/spec/epub-...ations-errata/