Still debatable though. Terry was playing Rolemaster in 1976 in Pete' Fenlon's original game. Terry might know when the game actually began using critical hits, but you could also try posting the question on the Rolemaster FB group. Coleman Charlton lurks there, and does answer historical questions from time to time.
Terry's post on Pete's game: http://www.ironcrown.com/ICEforums/index.php?topic=10647.msg220815#msg220815