Say we have a hotel named the Springfield Arms. The name itself is singular, since it refers to an individual hotel, but it ends with the pluralized noun “Arms”.
What is the correct way to write the possessive of this hotel’s name? Do you treat it as a singular noun overall ("the Springfield Arms’s address"), or as a plural noun ("the Springfield Arms’ address")?
I know the issue can be sidestepped by rephrasing, such as with “the address of the Springfield Arms hotel”, but I’m still curious what the actual answer is.
I found a couple similar questions (Possessive for name with implied plural, Possessive Form of a Proper Noun Ending in a Plural Noun Ending in "s"?), but the former was closed without answers and points to the latter, whereas the latter’s answers vary widely and I can’t discern any clear rule or convention. The latter is also closed pointing the a third question (see below), which doesn’t address mine.
To clarify, this question is not a duplicate of Which singular names ending in “s” form possessives with only a bare apostrophe? — the two questions are about entirely different things. That question asks which singular names like “James” and “Aeneas” are subject to exceptions to rules about possessive forms with regard to sibilants; my question asks whether a compound singular name ending in a plural noun should be treated as singular or plural overall. That is not the same at all (for instance, regardless of the possessive rule used, there is no question that “James” is a strictly singular name).