information:classification, structural:scholar_edition
Dates

It is wise to exercise extreme caution with dates. Dates are more difficult to recall years after an event, and are more easily mistranscribed than other types of genealogical data. Therefore, one should determine whether the date was recorded at the time of the event or at a later date. Dates of birth in vital records or civil registrations and in church records at baptism are generally accurate because they were usually recorded near the time of the event. Family Bibles are often a source for dates, but can be written from memory long after the event. When the same ink and handwriting is used for all entries, the dates were probably written at the same time and therefore will be less reliable since the earlier dates were probably recorded well after the event. The publication date of the Bible also provides a clue about when the dates were recorded since they could not have been recorded at any earlier date.

People sometimes reduce their age on marriage, and those under "full age" may increase their age in order to marry or to join the armed forces. Census returns are notoriously unreliable for ages or for assuming an approximate death date. Ages over 15 in the 1841 census in the UK are rounded down to the next lower multiple of five years.

Although baptismal dates are often used to approximate birth dates, some families waited years before baptizing children, and adult baptisms are the norm in some religions. Both birth and marriage dates may have been adjusted to cover for pre-wedding pregnancies.

Calendar changes must also be considered. In 1752, England and her American colonies changed from the Julian to the Gregorian calendar. In the same year, the date the new year began was changed. Prior to 1752 it was 25 March; this was changed to 1 January. Many other European countries had already made the calendar changes before England had, sometimes centuries earlier. By 1751 there was an 11-day discrepancy between the date in England and the date in other European countries.

For further detail on the changes involved in moving from the Julian to the Gregorian calendar, see: Gregorian calendar.

The French Republican Calendar or French Revolutionary Calendar was a calendar proposed during the French Revolution, and used by the French government for about 12 years from late 1793 to 1805, and for 18 days in 1871 in Paris. Dates in official records at this time use the revolutionary calendar and need "translating" into the Gregorian calendar for calculating ages etc. There are various websites which do this.