The same phenomenon exists with Yiddish names. In Yiddish, "Nissl" might be a nickname for either Nisan or Natan; "Khanan" (Chono) could be for Elkhanan or Yokhanan; "Etta" and "Ita" could be diminutive for either Esther or Yehudit. If you only know the nickname, there is no way to determine the full name.