When you migrate a SAS data set that was sorted with the NODUPKEY option, you can either use the default behavior or specify the KEEPNODUPKEY option.

Under the default behavior (without the KEEPNODUPKEY option), the SAS data set retains its sort indicator in the target library. However, the NODUPKEY attribute is removed, and a warning message is written to the SAS log. This is the default behavior because SAS data sets that were sorted with the NODUPKEY option in previous releases might retain observations with duplicate keys. You can re-sort the migrated SAS data set by the key variables in PROC SORT so that observations with duplicate keys are eliminated and the correct attributes are recorded.

If you specify the KEEPNODUPKEY option, you must examine your migrated data to determine whether observations with duplicate keys exist. If so, you must re-sort the SAS data set to have the data and NODUPKEY sort attribute match.