Powell put it together when he was 19, and most of it was compiled from open U.S. military and government manuals. He later distanced himself from the book after he found religion and shifted his moral views.

There are some outdated or sketchy parts, sure, and as far as I understand some of the later editions were edited (see my comment for the original glossary from my copy), but that doesn’t mean we throw the baby out with the bathwater. It’s still quite relevant.