if there are multiple codes present the display will only display the last (most prominate) code. If you want to see any other codes you will have to go to the pedal dance and get the ecm to display the codes through the MIL or hook up a laptop and run diagnozer and see what other codes are present actively.
The E23 code is probably being detected when key is turned on so it would be prominate first, the spark plug or cam/crank sensor codes would not display until the engine is running or possibly if they would be the only code stored in ecm memory.