Unfortunately, RAID does not always assure that data are available for the operating system and users.
A pointer to a file could be wrong, for example, or pointers within the file structure could be wrong.
Incomplete writes, if not property recovered, could result in corrupt data.
Some other process could accidentally write over a file system's structure, too RAID protects against physical media errors, but not other hardware and software errors.
As large as the landscape of software and hardware bugs is, that is how numerous are the potential perils for data on a system