In looking into Europe/Rome, I see there is the following rule: # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone Europe/Rome 0:49:56 - LMT 1866 Sep 22 (line 1660, europe, tzdb-2019a) In reading the page referenced in this 2016 thread on historical Italy time zones (https://mm.icann.org/pipermail/tz/2016-October/024363.html <https://mm.icann.org/pipermail/tz/2016-October/024363.html>), it states: "Regio Decreto del 22 Settembre 1866 n° 3224 di Re Vittorio Emanuele II ( in vigore dal 12 Dicembre 1866 ) Il servizio dei convogli nelle ferrovie, quello dei telegrafi, delle poste, delle messaggerie e dei piroscafi postali nelle Provincie Continentali del Regno d’Italia, verrà regolato col tempo medio di Roma a datare dal giorno in cui sarà attivato l’orario delle strade ferrate per la prossima stagione invernale 1866 – 1867.” (source: http://www.ac-ilsestante.it/MERIDIANE/ora_legale/ORA_LEGALE_ESTIVA_IN_ITALIA... <http://www.ac-ilsestante.it/MERIDIANE/ora_legale/ORA_LEGALE_ESTIVA_IN_ITALIA...>) This implies that the law went into effect on 12 December 1866, rather than the date of the decree (22 Sep 1866). This is further supported by this source: https://web.archive.org/web/20070824155341/http://www.iav.it/planetario/dida... <https://web.archive.org/web/20070824155341/http://www.iav.it/planetario/dida...>, which states: "In Italy in 1866 there were 6 railway times (Torino, Verona, Firenze, Roma, Napoli, Palermo). On that year it was decided to unify them, adopting the average time of Rome (even if this city was not yet part of the kingdom). On the 12th December 1866, on the starting of the winter time table, it took effect in the railways, the post office and the telegraph, not only for the internal service but also for the public. Moreover, without any particular law, but on a free initiative of the main Italian cities and as a consequence of the practical advantages of tying the railway time to the city time, and also for patriotic reasons ( Rome was not part of kingdom) it was decided to use the Rome time in public and private life producing thus a national time. Milano set the public watches on the Rome time on the same day (12th December 1866), Torino and Bologna on the 1st January 1867, Venezia the 1st May 1880 and the last city was Cagliari in 1886.” I wonder if the rule should be modified to 1866 Dec 12, instead of 1866 Sep 22? Stephen Trainor