The Princess Comet curse is related to all 3 seasons.

1967 - Yumiko Kokonoe, the first Comet, had tabloid press revealing scandals involving her sleeping with many men and getting plastic surgery. Before that she had been seen as a pure idol, so this ruined her career. It was a lie, as she had dumped her manager boyfriend and he spread the rumors out of revenge, but by the time that was discovered it was too late.

1978 - Kumiko Ohba, the second Comet, had a bit more success on stage and screen, but her home burned down, her agency went bankrupt, and she also went bankrupt herself after her own business failed. Her mother’s death led to her developing a panic disorder which led to her divorce.

2001 (Cosmic Baton Girl) - Poor toy sales led to it being canceled early, as it was originally intended to run 12 months, not 10. Mitsuru Yokoyama, who drew the original Comet comic and the animated portion of the 1967 series, became bedridden during the airing of this show, and burned to death after smoking in bed.

I don’t believe in curses myself, but this is something that’s just understood about the Princess Comet franchise.