The study of Thai Occupation revenues of Northern Malaya (Trengganu, Kelantan, Kedah and Perlis) during 1943-1945 is not easy.
The general lack of interest in collecting revenues in the years after WW2, combined with the scarcity of available material did not help in the dissemination of any knowledge on the subject.
In the start of this tread, I show the Trengganu ship revenue set of 15 stamps with margins, I obtained in a sale of some of Jim Czyl's material 8 years ago.
Together with the set was the typed note shown below. I do not know who typed the note (Jim?) but the note could be from the 1950's
Now with the internet available, studying unknown stamps is becoming so much easier, even if direct knowledge on the stamps do not exist. Also printing records have never been uncovered up till now.

Some analyses of the typed note.
1. Between the 2 value tablets on the bottom of the stamps is clearly stated "Trengganu Revenue" Trengganu is a state in Malaysia at the east coast bordering the South China Sea)
2. The top line of the stamp shows Thai language, clearly indicating a Thai occupation stamp.
The Occupation by the Japanese of Sarawak started Dec 16, 1941 end ended with the British troops surrender on April 1, 1942
The 4 Malayan northern states were ceded by the Japanese to Thailand on October 18, 1943. The ship stamps were printed I guess in 1944. The few used samples show cancellation dates between June 1944 and September 27, 1945.
3.The Japanese troops in Malaya never destroyed any stamp stocks. They needed taxes urgently to support their war. Lots of pre-war Malayan stamps (mainly postal) were overprinted with Japanese characters and or surcharged to the great delight of collectors of Japanese occupation stamps.
4. On the note its stated that a Janet van den Berg found the stamps in Tokyo. I have some other items acquired in Japan and I believe that at the tumultuous end of the war in 1945, some material ended up in Japan.
5. I wished Janet van den Berg had bought for me in Tokyo a large bunch of sets. The $0.75 she paid is quite lower than the $1000++ per set at this moment