So, again, are we aiming for high correctness or high comprehension? "Company" makes sense because you can have a "company of five participants" and they can do something, e.g., select a wine pairing menu at a restaurant, but a corporation is typically "a thing".
Everyone who understands English at a professional level (and probably even lower levels, too - or perhaps especially those) will understand what you mean if you say "the corporation announced their financial report last weekend", but it won't be the correct use of "their", as far as I'm aware.
Similarly you can't, as far as I understand, append an "s" to describe a relationship of an inanimate thing, e.g., this would be incorrect: "the corporations employees went to the summer party" again because "corporation" is a thing. But on the flipside phrases like "the employees of the corporation went to..." sound a bit too - what's the word - posh?
> a corporation is typically "a thing".
What is "a thing", exactly ? Corporations are certainly ambiguous in that regard: they have legal personhood[1] and even free speech[2] in US, apparently.
In the other hand, no corporation ever really "announce its financial report". Someone does it on behalf of the corporation, technically.
[1] https://en.wikipedia.org/wiki/Corporate_personhood [2] https://en.wikipedia.org/wiki/Citizens_United_v._FEC
I would argue that stuff like this reveals that "proper English" is in fact incorrect. :)
> but it won't be the correct use of "their", as far as I'm aware.
Yes, yes it will be.
See collective nouns, and "Metonymic merging of grammatical number" https://en.wikipedia.org/wiki/Collective_noun
> this would be incorrect: "the corporations employees went to the summer party" again because "corporation" is a thing
You can easily say "the corporation's financial report for Q4 was worse than predicted".
I think you're focusing too much on specific and hyper-specific rigid rules in a single textbook. As others said, prescriptivism vs. descriptivism. Descriptivism is always better, as it describes how language works and may evolve. Prescriptivism assumes languages are rigid unchanging things that can be precisely described.
The full rules for a working language take people years to learn at universities, and they are never as simple as "an inanimate object can't have a possessive form with 's".
Prescriptivism also works in schools/learning as it helps people not to drift too much from the norm. But too many take it to heart.