The local rate for post cards as well as those to Labuan and Brunei was fixed at 1c in the middle of 1891. But by 1892, the 1888 1c stamps were running out. So in 1892, the 4c stamps surcharged with "1 cent" and by 1893, the 5c stamps were similarly surcharged.
Update: A used sheet of 50 with a different setting as seen by the position of "1" in relationship to "cent" below. It was cancelled by favour at the Sandakan post office with the concurrent 19 bar cancel.