in these settings (you are showing in your screenshot) give the apps you need specific led behaviours and also change their speed etc.
then press on the "test" button and switch your screen off (now the led should light up the way you managed it). From now on the led should work for these apps
this procedure works for me everytime when I update the cm 10.2 rom I am using (temasek's rom)
by the way which missed events do you mean? I've never tested the notification led on anything other then messaging apps like facebook, email, calendar etc.