A warrant officer who has been considered for promotion by a selection board convened under , but not selected, shall be considered for promotion by each subsequent selection board that considers officers in his grade (or grade and competitive category) until he is retired or separated or he is selected for promotion. However, the Secretary concerned may, by regulation, preclude from consideration by a selection board by which he would otherwise be eligible to be considered, a warrant officer who has an established separation date that is within 90 days after the date on which the board is convened or an approved retirement date.section 573 of this title