If, subsequent to compliance with an order for discovery under the provisions of sections 29-1912 to 29-1921, and prior to or during trial, a party discovers additional material which the party would have been under a duty to disclose or produce at the time of such previous compliance, the party shall promptly notify the other party or the other party's attorney and the court of the existence of the additional material. Such notice shall be given at the time of the discovery of such additional material.