OBD II engine management waits until it sees a fault still exist after two driving cycles before it is considered it a matured fault and turns on the check engine light. A driving cycle varies a bit from manufacture to manufacture, but basically it looks at warm up, cat. function, air injection, EGR ,various engine loads and oxy. sensor data. The full data picture takes about 20 minutes to complete the computer's view. If someone did short back and forth to work cycles they could go for weeks with out setting a check engine light. The only conditions that sets an immediate light are those that the computer sees as ,catalyst damage is emminent. If your misfire has gone away most likely you have an aging oxy. sensor code. The only fix is a new sensor. Good Luck!