For a fixed yield issue, an issuer may treat any date as a computation date. For a variable yield issue, an issuer:
(i) May treat the last day of any bond year ending on or before the latest date on which the first rebate amount is required to be paid under paragraph (f) of this section (the FIRST REQUIRED PAYMENT DATE) as a computation date but may not change that treatment after the first payment date; and
(ii) After the first required payment date, must consistently treat either the end of each bond year or the end of each fifth bond year as computation dates and may not change these computation dates after the first required payment date.