Reddit reviews Collector's Encyclopedia of Depression Glass, 19th Edition

I still don't quite understand what you're considering weird about this. Perhaps you're unaware of the importance of depression glass? It has nothing to do with the mental condition, but is instead a product of an economical depression in the USA.

From Wikipedia:

\> Depression glass is clear or colored translucent machine made glassware that was distributed free, or at low cost, in the United States and Canada around the time of the Great Depression.

Depression glass ended up becoming a huge collector's item, and in the USA you'll see many auctioned estate sales and thrift stores with tables and tables of it. The book you posted is a guide to knowing the worth and importance of different styles of the glass, and as these values change from year to year, the reference guide is updated fairly often. They actually made it up to the nineteenth edition in 2009 before all publications by that author ceased within the next year.