When a VOLUME=REF subparameter refers to an earlier DD statement to use the same volume(s):

• For tape, the system copies the LABEL label type subparameter from the referenced DD statement; the copied label type overrides the label type on the referencing DD statement.
• For direct access, the system uses a LABEL=(,SL) or LABEL=(,SUL) subparameter from the referencing DD statement. If the referencing DD statement specifies any other label type, the system copies the LABEL label type subparameter from the referenced DD statement; the copied label type overrides the label type on the referencing DD statement.
• You do not need to provide a data set sequence number when the DD DSNAME parameter references all the members of a GDG or a single member through a relative generation number; the system obtains the data from the catalog. For all other data set names, however, you must provide the data set sequence number on the LABEL parameter.