Yes, there was. The post-credits scene in Scary Stories provided a hint or teaser for a potential sequel or added some additional context to the story.
One post - credits scary story could be about a haunted movie theater. After the credits roll, a lone janitor is left cleaning. Suddenly, he hears the sound of the projector starting up again on its own. He turns around to see the seats filled with shadowy figures that seem to be watching a movie that isn't there.
Well, they are effective because they use the context of the whole movie or viewing that just happened. You've been immersed in a certain atmosphere, and then the post - credits part subverts your expectations. It's like a final jolt of fear that stays with you. Think about it. You've been on an emotional roller - coaster during the movie, and just when you're starting to relax as the credits roll, the post - credits scary bit hits you and brings all that fear back, and sometimes even amplifies it.
In most cases, no. American fiction is focused on the main narrative and doesn't commonly incorporate post-credit scenes. However, there might be some rare exceptions in experimental or unconventional works.