; (ii) to amortize the plan’s unfunded liabilities in level annual installments over 25 years, beginning with the plan year in which the transition contribution rate is first established; and (iii) to amortize any subsequent changes in the legacy plan’s unfunded liability due to experience gains or losses (including investment gains or losses, gains or losses due to contributions greater or less than the contributions made under the prior transition contribution rate, and other actuarial gains or losses), changes in actuarial assumptions, changes to the legacy plan’s benefits, or changes in funding method over a period of 15 plan years beginning with the plan year in which such change in unfunded liability is incurred. The transition contribution rate for any plan year may not be less than the transition contribution rate for the plan year in which such rate is first established. (B) Multiple rates If different rates of contribution are payable to the legacy plan by different employers or for different classes of employees, the certification shall specify a transition contribution rate for each such employer. (C) Rate applicable to employer (i) In general Except as provided by clause (ii), the transition contribution rate applicable to an employer for a plan year is the rate in effect for the plan year of the legacy plan that commences on or after 180 days before the earlier of— (I) the effective date of the collective bargaining agreement pursuant to which the employer contributes to the legacy plan