Can birthparents contest a finalized and proper adoption?

Has anyone ever heard of a birthparent attempting to reverse the adoption AFTER finalization? In California, the law states that birth parents can't attempt to rescind their revocation of rights after finalization, but I know there are certain lawyers who would represent anyone with a bank account. Does anyone know of horror stories where everything was done right but the birthmom or pop went for custody after, say, 6 months?