If the catalog entry, the data set VTOC entry, or both, are missing, the data set is an unmatched data set. For an unmatched data set, the space management and backup exit (ARCSAEXT) is invoked if the exit is enabled. If the exit indicates that further eligibility testing be performed for this data set, DFSMShsm issues a message that this data set is unmatched. If the exit indicates that further eligibility testing not be performed, DFSMShsm issues no message. In either case, processing continues on the next data set.