The possibility of shutting down the wrong engine is always there. The US Army carried out a study back in 1998 amongst it's helicopter pilots, and found that:
Over 70 percent believe there is a potential for shutting down the wrong engine and 40 percent confirmed that they had, during actual or simulated emergency situations, confused the PCLs. In addition, 50 percent of those who recounted confusion confirmed they had shut down the "good engine" or moved the good engine’s PCL.
https://www.tc.gc.ca/eng/civilaviati...8-459-3388.htm