One of the things I have heard a Russian Orthodox priest note regarding Our Lady of Fátima is the days of the apparitions. May 13, June 13, July 13, August 19, September 13, and October 13, 1917 AD. These are all days that in the Julian calendar of the Russian Orthodox Church would be rendered as May 1, June 1, July 1, August 7, September 1, and October 1, 1917 AD. He considered that to be significant because the children would very likely not have known the Russian calendar system. These are also feast days in the Russian Orthodox Church. For example October 1 is the feast of the Intercession of the Theotokos.
https://en.wikipedia.org/wiki/Intercession_of_the_Theotokos