According to Oracle Document:

Refresh dates are tracked only for tables that are either a primary SOURCE or a primary target on tasks in a completed run of an execution plan. The DAC runs the full load command for tasks on which a table is a primary source or target if the refresh date against the table is null. When there are multiple primary sources, the EARLIEST of the refresh dates will trigger a full load or an INCREMENTAL load. If any one of the primary source tables has no refresh date, then the DAC will run the full load command.

According to Oracle Document:

Refresh dates are tracked only for tables that are either a primary source or a primary target on tasks in a completed run of an execution plan. The DAC runs the full load command for tasks on which a table is a primary source or target if the refresh date against the table is null. When there are multiple primary sources, the earliest of the refresh dates will trigger a full load or an incremental load. If any one of the primary source tables has no refresh date, then the DAC will run the full load command.