> Past/future doesn't matter Past/future does matter, as generally speaking it's possible to accurately convert between local time and UTC for times in the pas

> Past/future doesn't matter Past/future does matter, as generally speaking it's possible to accurately convert between local time and UTC for times in the past, but not in the future. There's a few exceptions where governments have retroactively changed timezones or DST rules, but at that point you've lost anyway.