Section 8A. For the purpose only of determining the time of the taking effect of a sentence which is ordered to take effect from and after the expiration of a previous sentence, such previous sentence shall be deemed to have expired when a prisoner serving such previous sentence shall have been released therefrom by parole or otherwise. Nothing in this section shall be construed to alter or control any provision of section one hundred and thirty-one or one hundred and forty-nine of chapter one hundred and twenty-seven.