Hi Bob,
no, I think that every somewhat knowledged collector will know that it is just old "patinated" rust, nothing else. There are a lot Central African weapons which are partially blackened but I don't know this feature by Tiv loop daggers. The black coating by your dagger seems to my eyes just old rust.
Personally I would clean it that it look nice like your other example. Just my humble opinion, others may think different.
Regards,
Detlef