Does anyone know / is it ever explained... 

1. why does John Park has different name (initial) tag than others? (his is the only one with hangeul letter) 

2. what is the function of that choker light in quiz room episodes? (other than aesthetic, maybe) 

3. who is the spy? did they even ever mess up the mission? 

4. was the milk box in the bus stop only an accessory/ paperweight for the newspaper? (i was theorizing it's a mission for spy lee yongjin because it's missing by the time they got back to the car lol)