The Protocol Error Report on the GETSTATUS CCC is intended to report on errors that have no other way of being detected unless the Device reports them. It is intended to cover parity error, CRC error, and anything else that means that a message from the Master was lost and the Master has no way of knowing it.
The Protocol Error Report on the GETSTATUS CCC would not cover the case of S5 errors, as they are more related to an unsupported CCC or Defining Byte which is not a protocol error per se. It is also not intended for situations when the Slave NACKs, because the Master will know that an error occurred when the Slave NACKs and recovers it. Errors like S0, S3, S4, and S5 are detected by the Master when the Slave sends a NACK response, and are recovered by using the appropriate recovery methods; as a result, they do not need to be reported via the GETSTATUS CCC.