The MVAR statement defines three symbols that reference macro variables. ODS will use the values of these variables as strings. References to the macro variables are resolved when ODS binds the definition and the data component to produce an output object. FIRST_YEAR and LAST_YEAR will contain the values of the first and last years for which there are data. Their values are assigned by the SYMPUT statements in the DATA step. SYSDATE9 is an automatic macro variable whose value is always available.
   mvar first_year last_year sysdate9;