A nice trio and a cover with TPO D9 which is not uncommon on this 1954 and also the preceding 1950 George Vl issue. There is a long gap between D8 and D9 which was partly filled by the 5 bar within an oval cancel listed under Jesselton. There were no train mail cancellations postwar recorded in Proud's book until 1950 even though mail might have traveled that way with the limited service available due to war time destruction of bridges and tunnels.
This Railway TPO D11 was in use just over a year from July 1962 and then superseded when North Borneo reverted to its old name of Sabah.
Next week there will be a few nice Brunei fiscals and after that a series on Brunei JO including eventually some rare sheets of 50 overprinted.