Those Darn Articles, Part 5: Aberrations

[NOTE: For earlier parts in this series, see Part 1, Part 2, Part 3, and Part 4.]

The anomalies of the definite article continue with this post.

Most organizations do not use an article when spoken or written in their complete or abbreviated form. Examples include:

• "I work for Hewlett-Packard" or "I work for HP."
• "This drug is made by Bristol-Myers Squibb" or "This drug is made by BMS."

Unfortunately for those trying to learn English, many exceptions exist:

• "I visited the Federal Bureau of Investigation" or "I visited the FBI." 
• "She is a member of the National Association for the Advancement of Colored People" or "She is a member of the NAACP." 

Then some organizations use the article in their full name but not in their abbreviated one. Examples:

• "Have you gone to the Metropolitan Museum of Art?" but "Have you gone to MMA?"
• "He  attended the University of Southern California" but "He attended USC."

Finally, some entities whose names are structured in a syntactically identical way do not agree on how their abbreviated forms should be expressed. These examples from the official websites of the New York City Department of Environmental Protection (DEP) and the New York City Police Department (NYPD) are proof:

• DEP must comply with various state and federal laws.
• Commissioner Raymond Kelly is a 43-year veteran of the NYPD.

Why DEP but the NYPD is not easy to explain. Saying "I work for the DEP" sounds strange, yet saying either "I work for the NYPD" or "I work for NYPD" sounds equally acceptable to the native English speaker. As many nonnative speakers tell me, you have to get a feel for the article because knowing the rules alone just won't do.