1978 November 1979 February 1981 September 1982 December 1983 December 1984 February 1984 July 1984 August 1985 May 1986 June 1986 July 1987 March 1987 November 1988 March 1989 May 1989 October 1991 June 1993 April 1994 August 1994 December