There is no specific number. It all depends on what shows are good. Should a bunch of new series come out on year that nobody likes, many new series will come out to follow. That year, there would be many TV series. However, a year that has many great TV series that everybody watches would have little new series, thus having less TV series that year.
The series ended in 2004. It started in 1994.
1995
1972
1979
1958
1972
1948
1990
1974
1994
2010
1994