jonesetc parent
You would still store both future times with offset. When calculating an offset for a future time you take the future time and the zone together to determine the exact time with offset. DST is predictable.
> DST is predictable
No it isn't.
* Europe postponed planned DST abolition due to COVID19: https://www.timeanddate.com/time/europe/eu-dst.html
* Argentina had a period of deciding each year what the DST dates would be until one year they just decided not to: https://en.m.wikipedia.org/wiki/Daylight_saving_time_in_Arge...
* Morocco and Yukon, Canada made updates to their DST policies earlier this year: https://mm.icann.org/pipermail/tz-announce/2020-April/000058...
DST schedules change several times each year, often with little prior notice. They changed in North America in 2007, which caused a lot of pain for software that thinks DST is predictable, such as Microsoft Exchange.