Ah, I had forgotten about the regional subdivision syntax from BCP 47 and the Unicode standard. The name:en-US-NC=* and name:en-US-VA=* I had previously used turn out to be invalid locale codes, so I changed them to name:en-u-sd-usnc=* and name:en-u-sd-usva=*, respectively. In theory, these extensions should be recognized by any software that correctly parses BCP 47 syntax, but most software relies on much more primitive regular expressions that will reject extensions.
Some languages like Gallo have no choice but to use an extension code, but for more common languages, a renderer is less likely to label places according to such a slight locale variant. While official_name:en-US-u-sd-usak=* is more precise than reg_name=* or reg_name:en=*, this is the kind of detail that normally belongs in a dictionary or gazetteer rather than a map. Unlike the gulf, the mountain only really pertains to a single region, making the national/regional tagging scheme more attractive. I suppose we could set reg_name:wikidata=* to a lexeme ID if you feel that reduces ambiguity.
If you’re referring to the name:US:BGN=* key I floated earlier, this approach would allow us to be very specific about who uses which name, but it would be pretty much only for the edification of fellow mappers, so uptake by data consumers is kind of beside the point. It would be a different story if we have a whole set of features whose names are strongly tied to a particular naming authority. For example, there are multiple schemes for abbreviating the names of U.S. states and territories, so in theory I could’ve tagged short_name:US:AP=* instead of short_name=* plus source:short_name=Associated Press. Let’s save that thought for if he issues an executive order systematically nicknaming each of the countries he deals with like he nicknames his political rivals.