Backward references: If a later DD statement in a job refers to a DD DUMMY statement when requesting unit affinity (UNIT=AFF=ddname) or volume affinity (VOLUME=REF=*.stepname.ddname), the system assigns a dummy status to the later DD statement.

Overriding a procedure DD statement: Coding DUMMY on a DD statement that overrides a DD statement in a procedure does not nullify symbolic parameters on the overridden DD statement. You must assign values to, or nullify, symbolic parameters on the overridden DD statement as described in Using system symbols and JCL symbols.

If the overriding DD statement contains a DSNAME parameter other than NULLFILE, a PATH parameter other than /dev/null, or a SUBSYS, SYSOUT, *, or DATA parameter, the system nullifies a DUMMY parameter on the overridden DD statement.

Data sets concatenated to dummy data sets: The system treats data sets concatenated to a DUMMY data set as dummy data sets in that I/O operations are bypassed. However, the system performs disposition processing and allocates devices and storage for any concatenated data sets.