There's a need for another identifier for 5-digit add-on barcodes for price encoding.

Some books have two barcodes, ex 9784805310908 and 50895, these are frequently separate, and while some machines might read it as one EAN-18 others will not,

This is common in some countries and unheard of in others.

Bookland Add-On Code
which has it's own specification:
https://en.wikipedia.org/wiki/EAN-5

more info: https://barcode-labels.com/solutions/upc-labels/book-labels/

example release: https://bookbrainz.org/edition/cd0934ad-c790-4bfe-a0c6-d49072230d9d