effective date of the amendment), and (IV) the class was closed before April 5, 2017, or the plan is described in subparagraph (C). (C) Plans described A plan is described in this subparagraph if, taking into account any predecessor plan— (i) such plan has been in effect for at least 5 years as of the date the class is closed, and (ii) during the 5-year period preceding the date the class is closed, there has not been a substantial increase in the coverage or value of the benefits, rights, or features described in subparagraph (A) or in the coverage or benefits under the plan described in subparagraph (B)(iii) (whichever is applicable). (D) Determination of substantial increase for benefits, rights, and features In applying subparagraph (C)(ii) for purposes of subparagraph (A)(iii), a plan shall be treated as having had a substantial increase in coverage or value of the benefits, rights, or features described in subparagraph (A) during the applicable 5-year period only if, during such period— (i) the number of participants covered by such benefits, rights, or features on the date such period ends is more than 50 percent greater than the number of such participants on the first day of the plan year in which such period began, or (ii) such benefits, rights, and features have been modified by 1 or more plan amendments in such a way that, as of the date the class is closed, the value of such benefits, rights, and features to the closed class as a whole is substantially greater than the value as of the first day of such 5-year period, solely as a result of such amendments. (E) Determination of substantial increase for aggregate testing on benefits basis In applying subparagraph (C)(ii) for purposes of subparagraph (B)(iii)(IV), a plan shall be treated as having had a substantial increase in coverage or benefits during the applicable 5-year period only if, during such period— (i) the number of participants benefitting under the plan on the date such period ends is more than 50 percent greater than the number of such