One of the most significant provisions in the Supplementary Uninsured/Underinsured Motorist Endorsement—New York (the SUM Endorsement)—promulgated and adopted by the then-entitled New York State Insurance Department, now known as the Department of Financial Services) as Regulation 35-D, effective Oct. 1, 1993 (see 11 N.Y.C.R.R. §60-2.3, et seq., amended most recently on May 11, 2018; Aug. 1, 2017; June 28, 2017; and April 16, 2013.), is the “Condition,” currently set forth in paragraph 5(b), which has become known as the “offset” or “reduction in coverage” provision, and provides, as follows:

“Regardless of the number of insureds, our maximum payment under this SUM endorsement shall be the difference between:

(a) the SUM Limits; and