Yes there are experimental cases in the CS Exam
Yes, it's true. There are up to two (sometimes one, sometime none) cases which are experimental.
These experimental cases are newly (pilot) introduced cases. They put them first and see how students and SPs perform, if they see consistent results and no technical/content problems with it then they approve it.
However, these are not necessarily your worst cases. They are randomly introduced and you'll never know which were the cases that were experimental.
Nevertheless, we can argue that "usually" they are the lowest performance cases, because, since they are "newly introduced", it's likely that the case has some wrong settings as it's not yet tweaked and modified or standardized. For example, if the SP was unusually angry and non-compliant, perhaps, that was an experimental case as they later on tell the SP to level down his degree of anger and non-compliance as they discover that all students are failing that case.