Number of NCFs that have been received with the reason code set to "unknown".

These are NCFs with a reason code this receiver transport does not recognize. After a delay (set by configuration option for NAK suppress interval), it resends the NAK. This counter should never be greater than 0 unless applications linked with different versions of Ultra Messaging software coexist on the same network. This method returns a value from the nth set of statistics encapsulated within this object.