Two or more insurers who, by virtue of their business associations in the United States, represent themselves to be or are customarily known as a “group” or similar insurance trade designation may make the same filings or use the same rates for each such insurer subject to the provisions of § 2503 of this title, and nothing contained in this chapter shall be construed to prohibit an agreement to make the same filings or use the same rates and concerted action in connection with such filings or rates by such insurers. This section shall not apply to 2 or more insurers who are not under the same common executive or general management or control and who act in concert in underwriting groups or pools.