1977 December 1978 May 1978 August 1979 March 1980 April 1981 March 1981 December 1982 August 1983 December 1984 August 1986 March 1988 February 1991 September 1994 March 1994 April 1995 June 1995 October 1998 November 2002 June 2002 July 2004 October 2005 April