Three crashed drones have been found in South Korea suggesting that many more have traveled into and back out of South Korean airspace. One of these Unmanned Ariel Vehicles crashed near Samcheok, which is quite a bit south of where I worked, already 80 or more kilometres south of the border.
Arirang video - autoplay - on the subject,
Dong-a Ilbo, which called the UAVs suicidal,
and the Marmot's Hole on the subject.