To everybody travelling to Korea at some point for the screening:
Check the flight itinerary given by your agent and make sure it mentions the code HK1 and not HL1! HK is a confirmed seat and HL is standby.
Probably not so much of an issue on a direct flight to ICN but when you depart from an airport which has no direct flights (as AMS-MAD-ICN in my case) KAL will simply put you on standby in case the flight to MAD is fully booked!
I remember reading a previous post about this but another code was given then. Because of that I did double check with my agent and they informed me that all seats were all confirmed even though this was not the case.
There I was at the airport fully prepared and ready to go...I never left and no comment from KAL or my agent other than "you will be too late for the screening"! I even offered to catch a flight to LHR since they depart from there every day so I would still make it on time but there was no interest
So, avoid indirect flights and for all those who make it to ICN, best of luck!