retroactive
adjective formal uk/ˌret.rəʊˈæk.tɪv/ us/ˌret.roʊˈæk.tɪv/ (also retrospective)
有追溯效力的;溯及既往的
If a law or decision, etc. is retroactive, it has effect from a date before it was approved.
the first British law to have retroactive effect 第一部有追溯效力的英国法律