If you are creating an output data set, use the ID statement to copy values of the ID variables, in addition to the table values, into the output data set. Or, if the VAR statement is omitted, all numeric variables that are not identified as BY variables, ID variables, the DATE= variable, or user-defined regressors are processed as time series. The ID statement has no effect when a VAR statement is specified and an output data set is not created. If the DATE= variable is specified in the PROC X12 statement, this variable is included automatically in the OUTPUT data set. If no DATE= variable is specified, the variable _DATE_ is added.

The date variable (or _DATE_ ) values outside the range of the actual data (from forecasting) are extrapolated, while all other ID variables are missing in the forecast horizon.