The full title of this book is: Early Canadian Military Aircraft, Acquisitions, Dispositions, Color Schemes & Markings: Volume 1, Aircraft taken on strength through 1920 with credits to the authors above and also illustrations by Andrew Tattersall (aircraft) and Terry Higgins (maps).
This is the first volume of an intended series which will cover all Canadian military aircraft taken on strength from 1920 through 1938 -- there are 58 such aircraft, and this volume covers the first seven. It's easier to visualize the contents if you know the "taken on strength" date is effectively the first date a particular type is brought aboard, and not just the date individual aircraft were received. The first seven types were taken on strength in 1920 but many aircraft of a type arrived after that date and served through 1929.