Learn English – Singular or plural verb after collective noun initialism

american-english

These company names are collective nouns. In general, in American English collective nouns almost always trigger singular verb agreement (after all, "Microsoft" is grammatically a singular noun, even if semantically it denotes an entity made up of many people). It is apparently much more common to use plural verb agreement in British English. It doesn't have anything to do with the size of the company.

Lots of good information here: Language Log on collective nouns, etc.

As a native speaker, I think I can answer both your questions!

Is there a reason why both versions are used with CDC, whereas most other initialisms seem to be used either with, or without, but not both?

In speaking and writing, a the is generally put before initialisms, which are spelled out when spoken: both for organizations like the FBI (eff-bee-ahy) and the NSA (en-ess-ay) and for countries like the US (you-ess) and the UK (you-kay).

We rarely, if ever, put a the before acronyms, which are spoken as a word: from NASA (nah-suh) to FLOTUS (flow-tuss) and POTUS (poh-tuss), they're all the-less.

Are both versions correct? That is, can CDC and the CDC be used? If so, are they interchangeable or do both have their own use case?

Generally, I only use or hear the CDC and the ATF, as befitting the usual American English pattern. Given the CDC's zealous use of just "CDC" on their own website, however, it seems they might have done away with the the themselves—possibly to seem more friendly given their "I am CDC" video.

However, as is typical with English, one says whatever sounds right and there's always flexibility and change over time.