[tz] [PROPOSED] Merge timezones that are alike since 1970

[Michael H Deckers]

    On 2021-05-28 17:10, Magnus Fromreide via tz wrote:

> The remaining superzones should also be stripped of any historical data
> since it would be incorrect for a whole lot more places in the zone than
> it is now.

*
    "Stripping" historical data is not possible in the tzif format.

    A timezone with name N will give, before 1970, the correct values
    for some location, but not necessarily for the location named N
    (if the location named N does not appear in the file backzone
    then they are guaranteed to be for the location N, but this cannot
    be detected from the tzif files).

    In my opinion, this is better than the previous choice (where the
    data before 1970 could be incorrect for every location agreeing
    with N after 1970).
*


> What will happen with all that data? It is quite interesting to read the
> tzdb sources as of now because of all the extra history.


    Yes, it is! The historical date are not (all) lost; most are kept in
    the file backzone and can be made to reappear with appropriate zic
    option (PACKRAT).

    Michael Deckers.