That system you described is quite rare - it would have to poll N databases of N possible events constantly to see if it should give you a reminder. Which is why none of the common calendar systems do that.
They just create events, which have a time zone and represent and exact point in time. And they don't change the event or when you get notified when you change time zones.
They just create events, which have a time zone and represent and exact point in time. And they don't change the event or when you get notified when you change time zones.