No Im sorry at least about the italian publication you are totally wrong and I can understand that th situation is much more confusing for a nonItalian like you  Both Libro doro della Nobilt Italiana and Annuario della Nobilt Italiana are and ever was private publications You are made a confusion whit the register kept in the former Consulta Araldica del Regno dItalia with the identical name of the first publication mentioned it is the Libro doro della Nobilt Italiana as well but has never been published nor updated because was a manuscript register for internal use of the former Consulta Araldica del Regno the past Italian State bureau in charge of heraldic matters After the fall of the Monarchy in Italy and with the new Republican Consitution  the Consulta Araldica del Regno has been closed in force of the XIV disposizione transitoria della Costituzione Italiana that state La legge regola la soppressione della Consulta Araldica As a consequence the Libro dOro manuscript register ceased to be updated BTW and now stay in the Archivio Centrale dello Stato in Rome where anybody can ask for and see it as you can check here in the Archive official site Im aware that recently under the direction of the same Archivio Centrale dello Stato two volumes of the manuscript has been published in a faxsimile or photografic reproduction by the same Archivio Centrale dello Stato those are the details Alle radici dellidentit nazionale Prosopografie storiche italiane Libro doro della nobilt I  II sotto la direzione di Enrico Cuozzo e Guglielmo de Giovanni  Centelles con la presentazione del Sovrintendente Aldo G Ricci Roma Societ italiana di scienze ausiliarie della storia  pp  cccc ill Riproduzione facsimilare per il  anniversario dellUnit dItalia   as you can check for yourself here in the cited Archivio Centrale dello Stato official publications catalogue Coming back on the two private publications the private httpenwikipediaorgwikiLibrodOrodellaNobiltaItaliana Libro dOro della nobilt Italiana has been published and updated almost regularly every  year more or less from more that a century since  to the present day the most recent nd edition was published in September  by the publisher the Collegio Araldico in Rome an ancient and reputed institution here the website The second publication you mentioned the Annuario della Nobilt Italiana has been a totally  private publication too founded in  by  Accademia Italiana dAraldica an other reputed institution and has been published almost regularly has well but just until  when the Accademia has been closed and the Annuario ceased definitely to be published due of the founder death After almost a century in the year  a small Italian publisher the SAGI publishing House here the website established a new publication with the same title and same style adding notables families and families not resident in Italy This new Annuario della Nobilt Italiana has been published irregularly every two or three years and the latest edition the fourth of the new publication dated  In Italy at the present exists some more publication or Nobility register like the Libro doro and  the Annuario  all privately published as well BTW they are the Elenco dei Titolati Italiani and the Albo doro delle Famiglie Nobili e notabili Italiana ed Europee Finally about your assertion that this small italian Dukedom or Duchy of San Donato is not mentioned as for the evident confusion you made about the Italian peerage books you should explain precisely at which publication you where referring to I dont know if you are aware that all the Italian Nobiliary register are not conceiveid like the British Peerage listing by TITLE but by FAMILY as a consequence if you are searching for a specific title or  fief you must firstly know the name of the family holders of the title If can be of any interest of you I cant assure that  about this Dukedom or Duchy for sure at least two of the cited publications the Libro doro della Nobilt italiana and the Elenco dei titolati italiani listed the families that hold the title whit the only difference between the two that  due of the complex situation exposed above about the two titles enlisted to the two different lines of succession    the Libro doro listed the first line of succession and the Elenco dei Titolati listed the other line I hope