This is a useful book for Papermaking and bookbinding but I take exception to it being called an encyclopedia or the definitive guide. Alas, while it does gives fair bit of information it leaves out important things like how to add sizing to your handmade sheets, though sizing is mentioned twice (even telling the papermaker to double it) but never giving detailed information. It does cover some interesting binding methods but leaves out far more like the Coptic stitch.
It covers western mold & deckle papermaking fairly throughly but only touches on eastern papermaking. It never covers preparing fibers not obtained from linters or recycled scraps.
This book is useful when combined with other research or books but it is not sufficient to be a standalone volume or to be considered an encyclopedia or definitive guide.