The accumulation of sick leave days from another district, when granted in accordance with this chapter, shall be credited upon receipt of the certificate of the prior employer. The days of sick leave so credited may be used immediately or if not so used shall be accumulative for additional leave thereafter as may be needed. The number of such days when granted shall be irrevocable by the board of education of the district.
N.J.S. § 18A:30-3.4