Where adjustments for overpayment or underpayment of assessments are made pursuant to §§ 607.3(d), 607.4(a)(2), and 607.4(b), credits for overpayments or charges for underpayments shall be based on FCA administrative operating expenses incurred in the applicable fiscal year and on funds required to be maintained pursuant to section 5.15 of the Act. Such credits or charges shall be applied to the next applicable assessment payment due during the current or subsequent fiscal year. Where such adjustments are made, the FCA shall provide the institution with a statement of adjustment at least 15 days prior to the date when the institution's next assessment payment is due. Adjustments in assessments shall be made in principal amount only. Overdue amounts under § 607.7 are not underpayments for assessment adjustment purposes.