Aarne Viisimaa - Birth date discrepancy

Nancy Visima: In Estonia Gregorius calendar came into force in 1918.
By the way Wikipedia use only Gregorius calendar. In Aarne Viisima profile have been shown up only difference between calendar systems and all is accurate.

Dear Nancy! Gregorian calender has been introduced in Estonia in 31.01.1918. The next day was 14.February. The difference in this moment was 13 days. But according to Gregorian system the year 1900 (leap year) had no such a date as 29th February. For this reason for dates in 19th century the difference is only 12 days - the same difference as between the birth dates in church records of Aarne Viisimaa and official papers nowadays

@Matti Viisimaa Thanks for the explanation, Matti! That explains why I have found so many date discrepancies for people compared to the church records. So this means that for any church record dates before 1900, I need to add 12 days? And for dates between January 1, 1900, and January 31, 1918, I should add 13 days?

@Nancy Visima I am not a very experienced person to compare the Julian and Gregorian calenders, but pragmatically the rule of 12 and 13 days differences, as you concluded, is principally working. Some links and explanations you can find in Wikipedia http://en.wikipedia.org/wiki/Gregorian_calendar.