Punctuation Mistakes: Possessive of S-Nouns Singular in Meaning

The rule that plural nouns ending in s form the possessive by adding only an apostrophe is well understood. For example:

the babies’ beds
the writers’ laptops
the witnesses’ testimony

The rule that nouns singular in meaning but ending in s also form the possessive by adding an apostrophe is perhaps not so well understood. For example:

mathematics’ rules
politics’ true meaning
Highland Hills’ late mayor
the United States’ role

Here are some examples from the Web that do not follow the rule:

Incorrect: The world beyond the United States’s borders can be conceptualized in any number of different ways. —Encyclopedia of American Foreign Policy, 2009.
Correct: The world beyond the United States’ borders can be conceptualized in any number of different ways.

Incorrect: Some of them have had weddings on the powder-soft sands of the Bahamas’s beaches. —Business site for wedding photographer.
Correct: Some of them have had weddings on the powder-soft sands of the Bahamas’ beaches.

Incorrect: The United States supports Belarus’s efforts to complete this commercial project as expeditiously as possible. —US government site.
Correct: The United States supports Belarus’ efforts to complete this commercial project as expeditiously as possible.

Incorrect: Cyprus’s parliament rejected its government’s bailout deal with the euro zone without a single vote in its favor. —The Wall Street Journal.
Correct: Cyprus’ parliament rejected its government’s bailout deal with the euro zone without a single vote in its favor.

Incorrect: It turns out that much of General Motors’s profits were derived from the sale of such parts through its Delphi division. —Environmental blog about electric car.
Correct: It turns out that much of General Motors’ profits were derived from the sale of such parts through its Delphi division. 

Source:www.dailywritingtips.com