ELi5: How is it that shows like South Park where episodes are made rapidly while the season is still going on, have scenes from those episodes in the intro?

Question

So, to my knowledge, episodes with a show like South Park are made not in advance, but one after the other. How is it that in the intro they have scenes and clips from those episodes?

In: Other

Answer 1

Probably the answer first given is correct, but I have a theory. They have lots of drawings and cuts of the characters made in advance of the story line, then write the episodes.