Author here. The piece is about bibliographic infrastructure, but the finding that surprised me most while building the dataset was language-specific: Catalan/Valencian (~10M speakers) jumped from near-invisibility in commercial aggregators to 8th place globally once nine national library catalogues were cross-referenced. Bengali, Thai and Urdu —all with substantial publishing industries— remained near the bottom, not because translations don't exist but because the institutions documenting them haven't been connected yet. The 97% figure (editions appearing in only one of 14 sources) held across every sample I could run. Happy to answer questions about methodology, source coverage, or why ISBN metadata is such a mess.

Proper ISBN id is a lot of unpaid expensive work. If you run small print, you may have sent like 10% of all your prints to libraries at your own expense. Putting unregisted pdf on web is for free...