If the amount of any refund exceeds the sums specified in G.S. 28A-15-6, 28A-15-7 or 28A-15-8, the sums specified therein and one half of any additional sums shall be the sole and separate property of the surviving spouse. The remaining one half of such additional sums shall be the property of the estate of the decedent spouse. (1973, c. 1329, s. 3.)