For South Korea, TZ has rules covering the years 1948 - 1988, and the text comments confirm that they were applied in 1948. Rule ROK 1948 only - Jun 1 0:00 1:00 D Rule ROK 1948 only - Sep 12 24:00 0 S Rule ROK 1949 only - Apr 3 0:00 1:00 D Rule ROK 1949 1951 - Sep Sat>=7 24:00 0 S Rule ROK 1950 only - Apr 1 0:00 1:00 D Rule ROK 1951 only - May 6 0:00 1:00 D Rule ROK 1955 only - May 5 0:00 1:00 D Rule ROK 1955 only - Sep 8 24:00 0 S Rule ROK 1956 only - May 20 0:00 1:00 D Rule ROK 1956 only - Sep 29 24:00 0 S Rule ROK 1957 1960 - May Sun>=1 0:00 1:00 D Rule ROK 1957 1960 - Sep Sat>=17 24:00 0 S Rule ROK 1987 1988 - May Sun>=8 2:00 1:00 D Rule ROK 1987 1988 - Oct Sun>=8 3:00 0 S But the zone data apply only rules from 1954 onwards while those for 1948-51 are ignored. Why is this so? This may be an error made in 2014, when the ROK rules for 1948-1959 were added, but it was forgotten to enter ROK into the 1954 line. Zone Asia/Seoul 8:27:52 - LMT 1908 Apr 1 8:30 - KST 1912 Jan 1 9:00 - JST 1945 Sep 8 9:00 - KST 1954 Mar 21 8:30 ROK K%sT 1961 Aug 10 9:00 ROK K%sT