On 2023-06-28 01:17, Stephen Colebourne via tz wrote:
I believe that if tzdb provided a fixed offset pre-1970, but one linked to LMT or common practice in that location
For timestamps before 1970 we could approximate LMT along with a time zone abbreviation saying that the UT offset is approximate. Something equivalent to this, say: Zone America/New_York -5:00 - c-05 1970 Jan 1 0u -5:00 US E%sT Zone Asia/Tokyo 9:00 - c+09 1970 Jan 1 0u 9:00 Japan J%sT The idea would be that a time zone abbreviation "c+NN" stands for "circa +NN", where the exact offset is unspecified. Software that cares whether an offset is approximate could look in the abbreviation for leading "c+" and "c-" (along with looking for "-00", which would continue to have its current meaning). POSIX allows "c+" and "c-" at the start of time zone abbreviations so this would pass POSIX muster. This sort of thing could be generated automatically from the current data.