Interesting! That sent me down a rabbit hole!
So the four are: Benin, El Salvador, Peru, Somalia.
But it’s only Peru that is actually mapped like this. The nautical boundaries of the other three are mapped like the rest of the world (presumably using the 12 mile limit set out in UNCLOS).
Would this class as a disputed boundary since signatories of UNCLOS wouldn’t recognize the claim? I had a look at OSM’s disputed territories page but it’s not listed. I guess because no other country claims the area as theirs?