This one PDF includes both volumes. This “reverse” approach to postal history looks at research from the other direction and discovers many heretofore undiscovered and unappreciated nuances of mail travel across the globe into the USA.
Vol. 1: Emphasis is placed on the ports of entry of incoming mail and resulting backstamps.
Vol. 2: Emphasis is placed on the ports of entry of incoming mail and resulting backstamps from Pacific and the Americas.