One reason for using GDGs is to allow the system to maintain a given number of related cataloged data sets. If you attempt to delete or uncatalog any but the oldest of the data sets of a GDG in a multiple-step job, catalog management can lose orientation within the data group. This can cause the wrong data set to be deleted, uncataloged, or retrieved when referring to a specified generation. The rule is, if you delete a generation data set in a multiple-step job, do not refer to any older generation in subsequent job steps.