On Korean Wikipedia article for DST https://ko.wikipedia.org/wiki/%EC%9D%BC%EA%B4%91_%EC%A0%88%EC%95%BD_%EC%8B%9C%EA%B0%84%EC%A0%9C , I saw the following lines (with machine translation):

>In Korea, the standard meridian of the time was 127° 30' in Tokyo during the period of 1955 to 1960, so it was 30 minutes earlier than it is today.

This information is different from what's currently described in tz database and should be investigated.

Also, given the example of DST transaction in Japan, it might also worth investigating what did the "00:00[start]-00:00[end]" in Korean DST transaction mean at the time.