Prepositional phrase modifying multiple nouns

Question

I am working with a client on a website and he has submitted the text below which I believe is not written correctly. Although we know that there are five boroughs in NYC, it seems the five boroughs are also related to Nassau, Suffolk and Westchester. I have corrected it by adding "as well as" after "City of New York" but my client has asked me to use the original text. Is there a rule or clear explanation that I can cite to clearly explain why this is not the best sentence structure? Also, what is the term for the phrase "as well as" that separates the nouns after the preposition?

Text in Question: "We have appeared for decades in the five boroughs of the City of New York, Nassau, Suffolk and Westchester Counties"

Answer 1

Although the five boroughs of NYC are now coextensive with separate counties, your sentence needs to separate boroughs and counties in some fashion. If your client is unhappy with as well as, you can write:

We have appeared for decades in the five boroughs of the City of New York and in Nassau, Suffolk, and Westchester counties.

Even though Nassau County and Westchester County would be capitalized when used alone, in the plural the word ceases to be a proper noun and is not.

The noun phrase five boroughs of the City of New York seems both too formal and redundant. There are no other entities called boroughs in New York, but if there has to be an additional modifier, five New York boroughs should be plenty.