| Year | Countries |
|---|---|
| 1974 | |
| 1977 | |
| 1978 |
|
| 1979 |
|
| 1980 | |
| 1981 | |
| 1982 | |
| 1983 | |
| 1984 | |
| 1985 |
|
| 1986 | |
| 1987 |
|
| 1988 |
|
| 1989 |
|
| 1990 |
|
| 1991 | |
| 1992 | |
| 1993 | |
| 1994 |
|
| 2004 | |
| 2005 |
|
| 2010 |
|