Issue
Retired Knowledge articles are showing up in portal search
Cause
Search instance calling custom widget
Resolution
The behavior seen is due to custom widget. This custom widget is being called in the 'Search' instance (which is out of box) found at the link below:
/nav_to.do?uri=sp_instance.do?sys_id=e3cbcb70d7000200a9ad1e173e24d4ca
Out of box, the widget used is 'Search Page'. The solution is to call the out of box widget 'Search Page'.