Thank you. I noticed a minor error in the proposed rules, namely "Sep Sun>=20" should be "Sun Sep>=18" for 1960-09-18 to work. More important, the Wikipedia data for times before 1961 disagree with the tz database, which suggests that more corrections are needed. While we're in the neighborhood, it's completely implausible that Pyongyang faithfully mimicked Seoul time during and after the Korean war (which is what Shanks says), so let's remove that obviously-bogus guess. Attached is a proposed patch that tries to capture all this. Unfortunately I am puzzled by the Wikipedia text "1910년 4월: 동경 135° UTC+9:로 변경." This cites "여적 표준시 변경, 경향신문, 2000-08-14", a source that I cannot easily read. If Korea switched to UT+9 in April 1910, then why is there a later entry for 1912 that says "동경 135° UTC+9로 변경. 조선총독부 관보 제367 호(고시 제338호)"? That is, if Korea switched to UT+9 in 1910 why did they also switch to UT+9 in 1912? If you could clarify this point I would appreciate it. Thank you again.