Unfortunately, however, the supporting records have often not survived, in which case items such as the book might provide the missing piece of a puzzle that can complete a family tree.
Yn anffodus, fodd bynnag, yn aml nid yw'r cofnodion ategol wedi goroesi, ac os felly gallai eitemau fel y llyfr ddarparu'r darn coll o bos a all gwblhau coeden deulu.