In 1940 J. Haag-Pedersen, an employee of
in Asia, published
a 44 page booklet called "Postage Stamps of Manchoukuo
with Varieties". This book was produced in collaboration
with John V Sweet
of Harbin and was well reviewed by the philatelic press, and in
particular by the China Clipper.
This book is hard to find today and contains little that is not shown in Helen Zirkle's later work, Haag-Pedersen did however do much to bring some sanity to the proliferating number of printing flaws that at the time were being sold as varieties at inflated prices. The book is well written and easy to read, if you can find a copy - buy it!
The book was published in Mukden (Manchukuo) by the Koa Printing Company ©1940 .