in some countries admin_level=4 are on the coastline. This in my opinion would be the the right way to mark a subnational border.
In Somalia and Yemen (countries where I’m working on) admin_level=4 are on maritime borders, as the national borders.
As I’m checking the relations and add the int_name, could I change this without harming nobody’s vision?
That section in wiki pages is related to
CIT: “In the United States of America, NOAA nautical charts specify in Note X:”
So, there’s not a worldwide rule, but we should follow the single countries rules. I’m italian and I know here the maritime borders are applied just to the national borders.
I will try to investigate in the UN geoportal, but as the subnational borders are usually not a political matters, I don’t know if I can find an answer there.
[EDIT: checking against the UN geoportal, all the administrative borders are cut to the coastline. So I can’t get any information whether a country apply maritime boundaries to the admin_level 4/6 or not]
So, I think the definitive answer is asking to the local communities