Complex sentence: It's the first time that the Dutch Top 40 just had 11 number-one singles in one year, and the third time that there were no Dutch number one-singles, it happened in 1988 and 1990.
Split into simpler sentences: It's the first time that the Dutch Top 40 just had 11 number-one singles in one year. The third time that there were no Dutch number one-singles, it happened in 1988 and 1990.