When you specify no labels, the system checks the input tape to ensure that the first record is not a standard volume label (that is, the first 4 characters are not VOL1 in EBCDIC or ASCII). If the first record is a standard volume label, the tape is rejected with a message from the system directing the operator to mount the correct tape or a valid unlabeled tape. The various error conditions that can occur during label verification are explained under IBM standard volume label editor routines, ISO/ANSI volume label verification and editor routines, and Nonstandard volume label verification and editor routines.

The search for a standard label is the only mount verification performed by the system. Without labels, neither the volume nor the data set can be positively identified and the system assumes that they are correct. The operator checks the reel's or cartridge's external identification to ensure compliance with the mount message.