Working identifiers? You have metadata. The fact that Sony closed stores does not invalidate existing metadata.
identifiers is a index (catalog number) of specific sources found (used) to generate what you see, or log additional sources. indicated identifiers will restrict data collection to those with matches. A typical one is ISBN.
blank = search for anything
theducks:B42 would be a valid (but totally bogus
) identifiers entry that could indicate a shelf location in a personal Library