An advantage of being an UK member of the Sarawak Specialists Society is the circulating packet. I do not normally collect JO nowadays but the following items were offered at irresistible prices. The non overprinted Showa stamps were mainly in use from 1 October 1942 alongside the 1 line overprints which were issued in limited quantities. Eventually, they were withdrawn and their use was largely replaced by the April 1943 Meiji issue of 4c and 8c stamps. And after that the 3 line overprinted North Borneo 1939 stamps came out in September 1944 and also the available supplies of the Showa issue were overprinted for use very soon after.
5 April 1943
This 1s brown block of 4 depicts harvesting. It has the Proud Sibu JD1 with a date 5-4-18 in the Japanese regnal format which is the same as 5-4-1943. This box date type cancellation was in use from October 1942 and was then gradually replaced from June 1943 with a non boxed date in 3 lines. You can see a good example of this later type from Belait by clicking the link
here.
6 November 1942
This 3s green showing a power station has the regnal date of 6-11-17 which is actually 6-11-1942, an early date of use for this Showa issue. The town origin is not visible and it is possible that these came from a CTO sheet.
24 April 1943
4s green showing Admiral Tojo including a pair used on piece with the box date of 24-4-18 but without evidence of the town of origin.
This is the 2c red of General Nogi. Again, a partial cancellation of the bottom half of the cancellation with no trace of the town of origin.
1944
This overprinted 2s on piece has part of the second type of JO cancellation. The Japanese dynastic year 2604 can be seen and this translates to 1944.
? 6 December 1942
This non overprinted 1s has what is described as an "English cancel". The immediately prewar NB cancels were all double ringed. So a Sarawak town would be the most likely origin. The closest one in Proud's book is the one from Lawas but it is not a dead certainty but the date of December 1942 would be compatible.
December 1942
I thought I might as well include these non overprinted NB stamps which continued to be used for a short while after 1 October 1942 when the first JO stamps were issued. Before that date, both the NB 1939 issue and the War Tax overprints as well as non overprinted Sarawak and Brunei stamps were used with 1942 "English" cancellations. But these 2 here with the first type JO cancels are more uncommon.