When the board declares an additional earnings credit for a plan year, the board also may declare by plan amendment an additional annuity credit, for members and annuity beneficiaries who are receiving an annuity as of the date specified by the board pursuant to Section 25006, based on the annuity of the member and annuity beneficiaries for the plan year. The additional annuity credit shall be paid in a lump sum to the members and annuity beneficiaries on the date specified by the board. In addition to the considerations specified in Section 25006, prior to declaring an additional earnings credit, the board shall consider both of the following: