You can not use Typ, Slow and Worst libraries together to perform STA with IR-drop info. Because, the difference between these libs are in different transistor model, different temperature and different voltage.
You should have additional libs, that have difference only in voltage.
For example: define_scaling_lib_group { tcbn65lphvt_wc.db tcbn65lphvt_wc07.db }
Where both these libraries used SS model of transistors, 125C as a temp, and the first one was characterized at 0.9V and the second at 0.7V.