I would tend to treat a company name as singular and would therefore write the possessive form with 's. Now, my company refers to its international operations by placing the country name behind the company name; think: "Coca Cola USA" or "Coca Cola Germany". In these examples I would write, in similar fashion, "Coca Cola Germany's workers are happy". Unfortunately, we also operate in a number of countries that have plural names; think: Netherlands and Cayman Islands. What is the possessive form in these cases? Is it "Coca Cola Netherlands' workers are happy" or "Coca Cola Netherlands's workers are happy"? I nudge towards the latter being grammatically correct, however reckon the former to be more generally accepted — or easier on the eye. I'm not a native English speaker, so I am not always entirely capable of assessing what is "accepted" or "sounds right".
This is an area where English usage is very unsettled.
Generally when a proper name ends in s and looks like a plural, it’s at least acceptable to use just the apostrophe without an additional s. Netherlands’s definitely looks odd to me. Since Netherlands is an originally plural word treated as a singular, there’s an especially strong case for not adding the apostrophe-s.
Similarly, I’d say “Lever Brothers’ workers” when talking about the soap company rather than “Lever Brothers’s workers”, even though we'd say “Lever Brothers is” in the US.
As a question of actual practice, it depends how it is pronounced.
If it adds a pronounced s or z, then write it as ~s's
You have a boss, and he has a car. It is:
Your boss's car
If the the possessive doesn't add a pronounced s or z, then write it as ~s'
You have several bosses, and they share a company car. It is:
Your bosses' car
These are pronounced the same; i.e. bossez car. But there are variants.
Your bosses's car
Would be acceptable, but rarer. (Pronounced bossezez)
In England, Charles is both a first name, and a family name.
- Charles's coat belongs to Charles.
- The Charleses are a family with the surname Charles.
- The Charleses' house is where they live
These are all pronounced the same; i.e. Charlsez.
But there are regional and class variants.
- The Charleses's house is also where they live (pronounced Charlsezez)
- The Charles' house is also acceptable.
These are unusual but acceptable variants.