(a) No candidate shall lose his or her place on a register of eligible candidates by certification or rejection, except that the board may remove names of candidates from a register after they have remained on the register for more than two years.
(b) The board may, by its rules, provide for striking off names of candidates from open competitive eligible lists established as a result of continuous examinations after they have remained on the list for six months.
(c) The civil service rules shall provide for reinstatement to the register of eligibles, on recommendation of the head of the department, of persons who have become separated from the civil service or who have been reduced in rank, other than persons who have been removed for cause.
(d) The board may, by its rules, provide for restoration to the register of eligibles, those candidates who are terminated during the probationary period, but the general manager of the Personnel Department may not certify any candidate to the department or office which terminated the candidate except at the specific request of the appointing authority of that department or office.