A common sense approach which has been favoured for some years now, ever since the Kegworth accident with the Boeing 737, is that, having gone through exhaustive check and double check crew procedures involving the indications, a decision is arrived at. The SSL for the selected engine is then confirmed again by both crew and then, SLOWLY retarded whilst a check is made of the response of the remaining engine. If any doubt exists the SSL can be restored with minimal loss of Nr.
During training I have seen several candidates opt for the wrong engine but the above procedure prevents further trauma.