D.C. Code § 1-623.08

The period of compensation payable under the schedule in § 1-623.07 is reduced by the period of compensation paid or payable under the schedule for an earlier injury if: (1) Compensation in both cases is for disability of the same member or function or different parts of the same member or function or for disfigurement; and (2) the Mayor finds that compensation payable for the later disability, in whole or in part, would duplicate the compensation payable for the preexisting disability. In such a case, compensation for disability continuing after the scheduled period starts on the expiration of that period as reduced under this section.