You are right that it's not listed in the Nevada Checks and Chips book by Howard & Kregg Herz.
However, the chip is listed in The Chip Rack (page 60 in TCR-13) and also in the Campiglia & Wells book.

While the Herz book was a GIANT step forward in chip collecting when it was published in 1995, it didn't include every chip made up to that date. Your chip was one they didn't have or overlooked. Their book is now 16 years old, and has been eclipsed by the more recently published TCR and C&W books.