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This is a wonderful site devoted to the study of re-entries on postage and revenue stamps, with many images and ongoing research. This is one to bookmark !
This site not only has a wealth of NZ philatelic material relating to King George the VI but also with the overlapping issue periods has many interesting articles on the half penny 'fantail' pictorial, and information on postal rates of the time.
'New Zealand stamp images' A very comprehensive and detailed site , well worth adding to your favourite file as a reference.
Stampboards.com is lively forum on stamp collecting, it has a wonderful search engine which will find almost any discussion on stamps.