Hello, SomeoneElse, glad to here that you have interest about those question, here are something I need to pointed. 

0. I ask for NMSL that he revert those 4 changeset

148136531
148136722
148136944
148137209

1. If this is disputed boundary, then whether just add it to a city/province's relation in one country is justice? 

I noticed r17296617(VN claimed Paracel Islands) was added to r1891418(Da Nang) directly as outer member.  and r17296618(VN claimed Spratly Islands) was added to r1887959(Khanh Hoa Province) as outer member.

But r1891418 and r1887959 are boundary=administrative and this tag should be used to be the one representing actual control according to description mentioned in https://wiki.openstreetmap.org/wiki/Disputed_territories (it reference OSMF document)

In my point I don't means I opposite the r17296619 or because the relation are truly boundary=disputed. But if this is the case, I think it should also be allowed to establish a similar relation of China claimed region.

In addition, based on the idea of ​​​​equivalence, if there is no problem with the editing of CactiStaccingCrane this time, then I think that if other editors make a move to establish a boundary=dispute relationship and add Hainan Province as the outer changeset, it should also be retained. , like today