321J.18  Other evidence.
  This chapter does not limit the introduction of any competent evidence bearing on the question of whether a person was under the influence of an alcoholic beverage or a controlled substance or other drug, including the results of chemical tests of specimens of blood, breath, or urine obtained more than two hours after the person was operating a motor vehicle.
86 Acts, ch 1220, §18; 98 Acts, ch 1138, §23