You begin the post with a valid question then end with the answer. Bit confusing! …and rhetorical.
The DNG occupying force was the Australian Naval and Military Expeditionary Force (ANMEF).
I’ve only seen NWPI stamps with the Woodlarks 3 ring radio staion cancel from 1918 and the Kulumadau Papuan date stamp applied to the same stamps during 1918 – 19.