Must a change in beneficiary be registered with insurer?

H made W the sole beneficiary of his life insurance policy. He never remarried. After they were divorced, he neglected to change the beneficiary until 2 days before his sudden and unexpected death. His son by a previous marriage "found" a change in beneficiary form naming him the sole beneficiary. The form looks as though names and dates on the form have been changed. The form was mailed to the insurer but the policy was not changed prior to the father's death. The stepmother was the sole beneficiary on the policy at the time of death. Does the son have a valid claim?