Stories can initially appear insignificant to Instagram. But if anyone is holding a birthday party, you would not want to be overwhelmed with a hundred frames, right? So similarly, if the team of Brand A had attended a major event, and all of its team members would use its Instagram account, the followers of Brand A may get irritated when you overload unnecessary updates with their feeds, and thus, might unfriend you. But it is better if Brand A uses one story for an event and can post it to the participants.