Mamby, yang selalu bertanding di luar negeri, juga mempertahankan gelar melawan Thomas Americo di Indonesia serta melawan petinju Nigeria, Obisia Nwankpa, di Lagos sebelum menyerahkan gelar itu kepada petinju Amerika, Leroy Haley, karena kalah angka pada Juni 1982.
Mamby, who frequently fought overseas, also defended against Thomas Americo in his native Indonesia and against Nigerian Obisia Nwankpa in Lagos before relinquishing the title to American Leroy Haley in a split decision in June 1982.