Swami Vivekananda Jayanthi

India Post has released a Calendar for 2017 with a price of ₹100. The above picture shows the January Month as in the calendar. I noticed that "Swami Vivekananda Jayanthi" was marked in Green font as 19th January. 

To my knowledge, 12th January was the birth date of Swamiji. Just to be sure, I checked in Wikipedia in multiple topic and confirmed "I am correct"

Links I visited :

https://en.wikipedia.org/wiki/National_Youth_Day_(India)

https://en.wikipedia.org/wiki/150th_birth_anniversary_of_Swami_Vivekananda

Later, I also noticed National leaders and political party leader tweeting on 12th January, their pictures offering floral tribute to Swami. "Confirmed"

I wanted to raise this to the concerned official, so mailed this with pictures of calendar to Senior Postmaster - Coimbatore HPO. Today, I received the response and here it is as below :

http://www.drikpanchang.com/calendars/indian/jayanti/swami-vivekananda/swami-vivekananda-jayanti.html

Yes, I received a document containing the contents from the above link, so what does it say 

According to English calendar he was born on 12^th January 1863 into an aristocratic Bengali family of Calcutta. However his birthday is celebrated according to Hindu calendar and this day is known as Swami Vivekananda Jayanti. Vivekananda was born on Krishna Paksha Saptami after seven days of Paush Purnima. As Jayanti day is decided based on Hindu calendar, it is not fixed on Gregorian calendar like Rabindranath Tagore Jayanti and Mahatma Gandhi Jayanti which are celebrated on fixed day on Gregorian calendar.

However Indian government has decided to observe Swami Vivekananda's Gregorian date of birth as National Youth Day. Hence National Youth Day of India is celebrated each year on 12^th January since 1985.