If you use user labels, they must be created when the data set is allocated. They can be updated, but not added or deleted, during processing of a direct data set. When creating a multivolume direct data set using BSAM, you should turn off the header exit entry after OPEN and turn on the trailer label exit entry just before issuing the CLOSE. Turning off the header exit entry and turning on the trailer label exit entry eliminate the end-of-volume exits. The first volume, containing the user label track, must be mounted when the data set is closed. If you have requested exclusive control, OPEN and CLOSE issues ENQ and DEQ, preventing simultaneous reference to user labels.