I think tzdata timezone locations (like Europe/London) are fully sufficient, since they are tracking the clock everyone uses in that location. If the boundaries change, then so will the clock for everyone in that boundary, so the time probably won't be right regardless.
I think coordinates are not completely right, since the time context is mostly political/cultural, not geographic. I don't have examples but I can easily imagine a border region specifying some event in a time that is referencing the region across the border.
