DATES  -  PROBLEMS  IN  CALCULATING.

Inaccurate information supplied.
For example. a person listed in the 1901 census of population was also listed in the next census of 1911 but instead of being ten years older he was twenty-five years older.
 

Different formats used in different countries.
That is in Ireland we write ‘Day, Month, Year’ but in the United States of America the format is ‘Month, Day, Year’. So 11.9.2004 would be 11 September 2004 in Ireland and 9 November 2004 in the USA.
 

Ages rounded off
Some ages can be inaccurate, others can be rounded up or down.
First check on the rules for completing the relevant form.
        Unlike Irish Death Certificates some Death Certificates in the USA give the ages in years, months and days so for example a Death Certificate for a person who died 15 April 2003 age 1 year, 7 months and 4 days implies that the person was born 11 September 2001. Sometimes one finds it relates to the days between the two events possibly because the person is dead on the latter date. Of course like Irish Death Certificates ages given are not always accurate.
 

Date given is relative to a Saint’s feast or festival.
This is found in some early medieval documents.
 

The regnal year is used.
That is the year of the monarch's reign.
    Dates are given according to the year of reign of the English King or Queen.
This format can be found in deeds up to the seventeenth century, court records and legislation even up to the twentieth century.
For example Queen Victoria was crowned on 20 June 1837 so The Local Government (Ireland) Act, 1898 which established the county councils is referred to as 61 & 62 Vict. c.37.
 

Different Calendars - The civil year differed from the historical year.
Various calendars have been used such as the Jewish, Roman etc. and from Christian times a new church calendar with its fixed and moveable Feast Days and Saints' Days.
    In England, from about the late twelfth century until 1752 the Julian Calendar (called after Julius Caesar who introduced it in the Roman Empire) was in use and the civil and legal year began on the 25th of March nearly three months later than the historical year. The result is that in, for example, minute books of a Council or Corporation the minutes are recorded thus:
 

‘..... Att a G. A. Held &c THE 14th Day of January 1714.

    When the Gregorian Calendar (called after Pope Gregory XIII who introduced it in 1582).was adopted in England and Ireland in 1752 the legal year was moved back to the 1st of January. This had implications for dates between the1st. January and the 24th of March. Also 11 days were skipped (to make up for discrepancies due to leap years in the Julian Calendar and the introduction of the Gregorian calendar in the rest of Catholic Europe from 1582). Thus 2 September 1752 was followed by 14 September 1752. The Gregorian Calendar became known as the ‘new style’ calendar as opposed to ‘old style’ of the Julian Calendar.
    In practical terms this means that, for example, the above date ‘14 Day of January 1714’ should now become '25 Day of January 1715'.

    Thus the Battle of the Boyne which took place on 1 July 1690 is now referred to as having taking place on 12 July 1690.

    To avoid confusion some historians cite a document with a year in the ‘new style’ and the day and month in the ‘old style’ i.e. 14 January 1715 or alternatively 14 January 1714/15.