The most cited online reference for MLOs is the excellent website:
This author of this website is Simon Watt, a member of the China Stamp Society (CSS) and a frequent contributor to The China Clipper, CSS's official publication. On his website, Simon referenced the bible for Manchurian Local Overprints, a four volume booklet The Local Overprinted Stamps of Manchuria 1945-7 by Allen D Kerr.
Allen D Kerr's definitive work on MLOs is available from China Stamp Society.
https://www.chinastampsociety.org/books-on-chinese-stamps/lo ... item-27688
Volume I is the Third Printing of 2000 with corrections to prior printings
Volume II is the Third Printing of 1981 with a corrections sheet.
Volume III is the Third Printing of 2000 with a correction sheet
Volume IV is Third Printing of 2000 with a correction sheet.
The other frequently referenced catalogue is Stamp Catalogue of China by Shui-Hon Chan
Commonly referred to as Chan's catalogue, the 2 volume set is an indispensable tool for Chinese collectors. The listings include imperial Chinese issues, provincial issues, Japanese occupation issues, Shanghai and Treaty Ports, foreign post offices in China, Manchukuo, and Manchurian local overprints.
The China Stamp Society offers a 349-page album of Manchurian Local Overprints in PDF format on a DVD. Also included are two pages in Microsoft Publisher that can be used to create additional matching album pages and an annotated correlation between the Chan and Kerr numbering systems with much explanatory text.
https://www.chinastampsociety.org/dvds-on-chinese-stamps/a-n ... -/item-11
The China Stamp Society is an 85-year old society that offers auctions, stamps, covers, albums, literature, etc. on its site www.ChinaStampSociety.org Annual membership is $21 in the U.S., $24 in Canada, and $27 elsewhere.