participants for such plan year, by using the benefit formula in effect for each such participant for the first plan year in such 5-year period, by more than 50 percent. In the case of a CSEC plan (as defined in section 414(y)), the normal cost of the plan (as determined under section 433(j)(1)(B)) shall be used in lieu of the amount determined under section 430(b)(1)(A)(i). (H) Treatment as single plan For purposes of subparagraphs (E) and (G), a plan described in section 413(c) shall be treated as a single plan rather than as separate plans maintained by each participating employer. (I) Special rules For purposes of subparagraphs (A)(i) and (B)(iii)(II), the following rules shall apply: (i) In applying section 410(b)(6)(C), the closing of the class of participants shall not be treated as a significant change in coverage under section 410(b)(6)(C)(i)(II). (ii) Two or more plans shall not fail to be eligible to be aggregated and treated as a single plan solely by reason of having different plan years. (iii) Changes in the employee population shall be disregarded to the extent attributable to individuals who become employees or cease to be employees, after the date the class is closed, by reason of a merger, acquisition, divestiture, or similar event. (iv) Aggregation and all other testing methodologies otherwise applicable under subsection (a)(4) and section 410(b) may be taken into account. The rule of clause (ii) shall also apply for purposes of determining whether plans to which subparagraph (B)(i) applies may be aggregated and treated as 1 plan for purposes of determining whether such plans meet the requirements of subsection (a)(4) and section 410(b). (J) Spun-off plans For purposes of this paragraph, if a portion of a defined benefit plan described in subparagraph (A) or (B)(iii) is spun off to another employer and the spun-off plan continues to satisfy the requirements of— (i) subparagraph (A)(i) or (B)(iii)(II), whichever is applicable, if the original plan was still within the 3-year period described in