In Paul Eggert's proposal for Macao from 2018-05-10, we find +Rule Macau 1949 1951 - Apr Sat>=1 23:00s 1:00 D +Rule Macau 1951 only - Mar 31 23:00s 1:00 D with two successive switches to summer time at 1951-03-31 and 1951-04-07. The later switch has no effect, and can easily be omitted: +Rule Macau 1949 1950 - Apr Sat>=1 23:00s 1:00 D There are several similar cases in tzdb where the specification contains redundant data. For instance, Rule HK 1965 1976 - Apr Sun>=16 3:30 1:00 S Rule HK 1973 only - Dec 30 3:30 1:00 S with two successive switches to summer time at 1973-12-30 and 1974-04-21, the latter having no effect. In this case, removal of the redundancy would require an addtional Rule line, so concise notation could be construed as a reason for retaining the redundancy. Do we have a guideline for such cases? Michael Deckers.