If you reuse an esoteric unit name for incompatible devices (for example, the data was written when the esoteric unit name was for a group of 3420 device types, but the esoteric unit name is now used for a group of 3480 devices), DFSMShsm detects the incompatibility of the tape and the device type and replaces the reused esoteric unit name with the generic name of the old device.