[W]hy do they need to write down "adopted a leniency law at some later point of time"? Because in Korea case, the word "our sample period" means "1995-2002" already.
=> Assuming Korea is the early-adopter country, then all countries theretofore untreated before 1997 may serve as a counterfactual. This includes the countries never adopting a leniency law and those with impending treatment adoption periods.
I did some searches around but I still cannot clarify this word, I am wondering if it mean "control group" in the Difference-in-Difference setting.
And whether he means "all countries passed the laws before 1995, or after 2002, or never adopt the laws all belong to the control group?