And you need all the mapping rules for the past. Say, we got rid of daylight savings time starting next year. The year after that, what happens when you look at a time/date a decade before?
That handles the time "now". Assume within 3 years, a country changed timezones 2 times. If you rely on TZDB, you can never be sure "What happened on May <year> 16.00?". It happened in Turkey and it was a bad time to be a sysadmin.
