Last train after a K-pop concert in Seoul: why weekends are different

At most Seoul venues the Saturday and Sunday last trains leave 50 to 60 minutes earlier than on weekdays. And concerts are usually on weekends. Reading the weekday time and missing the train is the most common way a night goes wrong.
KSPO DOME (Olympic Park station), for example: the weekday last train is 24:38, but on weekends it is 23:49 toward Gunja and 23:53 toward Macheon. 24:38 means 00:38 the next night.
The last train can be signed toward the end of the line and still stop short. At Daehwa (Goyang) the final train is labeled toward Ogeum but only runs to Samsong, which is outside Seoul. Read the destination on the platform sign, not just the time.
If the venue is outside Seoul (Goyang, Incheon, KINTEX), decide how you are getting home before the show, not after.
This site reads the last trains for 13 venues off the operators' own timetables and publishes its corrections with dates.