Catalog routines uncatalog non-SMS generation data sets at roll-off time. Nonmigrated generations are scratched by DFSMSdfp. Migrated generations are scratched by DFSMShsm. The process of deleting migrated, rolled-off generation data sets depends on the SVC number used to access the IBM® catalog routines. SVC 26 (X'1A') must be used to call the IBM catalog routines. The catalog routines call the scratch function to delete the rolled-off generation data sets. If the SVC number used to invoke the IBM catalog routines is changed from SVC 26, DFSMShsm does not recognize the roll-off situation, and the migrated, rolled-off generation data sets are not deleted.