Or if you really want to be future proof, store the geolocation so you can try to figure out the jurisdiction for any changing regulations. Maybe they didn't change the date of the switch, but changed the timezone boundary on the map.

But, then I guess we might need to account for fractured societies and actually store some kind of organizational code for which belief system the event author adheres to? :-)

To me that an UI/UX issue.

Internally everything is stored and handled in TAI (better than UTC as no discontinuity) and translated from/to something else for human consumption.

I.e. for instance your should have logic to figure out what TAI period corresponds to "next month's meetings" if that's what the user wants, which you apply immediately on user inputs and then forget about DST, time zones, etc. in the rest of the code and storage.

Another benefit is that if your user was in New York but is now in London it is trivial and well-constrained to adjust to local time.