Considerations for using the SET statement

The symbolic parameters you define on the SET statement are assigned the specified values at the location in which the SET statement is encountered in processing the JCL.
If you use SET to define a value for a symbolic parameter that does not appear in the JCL, the system does not issue message IEFC657I, and there is no JCL error.
The SET statement is not executed conditionally. For example, if the SET statement appears in an IF/THEN/ELSE/ENDIF statement construct, the value is assigned to the symbolic parameter regardless of the logic of the construct.