Frequency of Krishna's appearances on earth
He appears here once in a day of Brahma, which means once every thousand Kali-yugas. Sometimes there are differences in His pastimes, but they're generally the same. There are unlimited pastimes going on, even now, on other planets within this universe and in unlimited other universes. The Srimad-Bhagavatam gives us a sample of Krishna's many incarnations and avatars, but it would be impossible to recount them all.
The version of the Srimad-Bhagavatam that's available to human society on this earth contains only eighteen thousand verses. On higher planets, where the lifespan and mental capacity of the inhabitants is far superior to ours, the Bhagavatam has many more verses.