Lester Caine wrote:
how do I ensure that normalization of 1970 data will match 1969 stuff?
By not discarding the imported data. If the imported data says the equivalent of "London time", then it should be stored that way, not as GMT. That way, if the time zone tables change, the imported data will be treated consistently with any further data that are imported later. It's unwise to require that time stamp conversion tables be the same on all platforms, and that they never change. That's not feasible for most nontrivial applications. Even if the tz database were perfect and complete for all past time stamps, such a requirement would still go awry with time stamps in the future: if someone now schedules a meeting for October 1, 13:00, Casablanca time, and Morocco changes its rules between now and then, software will mess up after the rule change if it blithely relies on UTC conversions that were computed before the change.