You're spot-on with your observations — Rob Cook's books (The Ludwig Book, The Rogers Book, The Slingerland Book, etc.) are widely considered the definitive print resources on those classic drum brands. While they haven’t been updated in years, they remain incredibly valuable because the companies they cover (at least in their original forms) haven’t existed for decades. So, you're correct — there isn’t much to update, unless new historical discoveries surface, which is rare.

Re:  Rob Cook's Slingerland Book

Be aware that there are many errors in this book, especially in the area of drum dating, attributes and fine details. 

With that caveat, this is still a very valuable resource and excellent starting point for those interested in the Slingerland Drum Company.  The history sections are quite good.

For vintage high hat and cymbal stand information you may check on the wonderful book on Walberg and Auge since they made a lot of that hardware for the major American drum companies.  The book is "Walberg & Auge: The History and Future of America’s Most Innovative and Unknown Drum Company" published in 2015 by Jeremy Esposito.  I collect bass drum pedals and have a few high hat stands that accompany the bass drum pedals.  Most folks are not very familiar with some of the eveolutionary "stubs" in high hat stand development.  Height adjustement and modern clutches were a big development as well as tilter development on cymbal stands.  Good luck!