Proper Apostrophe Usage with Initialisms: CCS' or CCS's?

Question

I work with a company whose name is frequently reduced to an initialism (acronym). Let's say the name is "Cool Computer Systems" (CCS). I am engaged in an ongoing, bloody battle with the marketing department, wherein they insist the following apostrophe use is correct:

Buy CCS' New Product.

Reading that line brings visions of crying 4th grade teachers and librarians to mind. I am quite certain that it should be written:

Buy CCS's New Product.

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UPDATE:

The examples are in title case because the sentence is the subject line of an e-mail.

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UPDATE:

Their argument is that "Systems" is plural. I say that plurality doesn't matter, because "Systems" is part of the name. The name as a whole should be handled as a singular entity, because the company is, in fact, a single, legal entity. Thus, the possessive form should be written:

The Emperor's clothes

Cool Computer Systems's clothes

CSS's clothes

Answer 1

According to the Guardian style guide:

The possessive in words and names ending in S normally takes an apostrophe followed by a second S (Jones's, James's), but be guided by pronunciation and use the plural apostrophe where it helps: Mephistopheles', Waters', Hedges' rather than Mephistopheles's, Waters's, Hedges's.

So I would likewise go by pronunciation write it as:

Buy CCS's New Product.

Or rewrite to avoid it the apostrophe altogether.

Answer 2

Seems that lawprose agrees with CCS's.

"Acronyms and initialisms. It doesn’t come up often (and it’s easily avoided), but the plural possessive of acronyms and initialisms follows the general rule. Take the singular {an MRI}, make it plural {two MRIs}, and add an apostrophe {the three MRIs’ role in the diagnosis}. If there’s a plural word in an initialism — as when Lloyd’s Register Drilling Integrity Services becomes the singular name LRDIS – treat the full initialism as a singular and make the possessive form singular {LRDIS’s contentions}."

From http://www.lawprose.org/blog/?p=1357

Answer 3

Clearly far too late to answer but in case anybody else has a similar query the OP is wrong, the marketing dept is right and so is David Schwartz.

The fact with apostrophe usage is it changes for words ending in sibilants.

So, it would be:

David's post.

But also:

Mr Schwartz' post.

So, it is Cool Computer Systems' new product, and not Cool Computer Systems's new product.

The answer is in how you say it.

So, the marketing people are right, it's CCS', not CCS's.