Dates 
It is wise to exercise extreme caution and skepticism with information about dates in our family history research. Dates are more difficult to recall years after an event, and are more easily mistranscribed than other types of genelogical data. Therefore, one should evaluate 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 reliable 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, at least, 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 perhaps 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. The 1841 census in the UK is rounded down to the next lower multiple of five years. Also, caution should be used when estimating a date for a husband’s death based on his absence from the census. A woman at home while her husband is away could be identified as head of household or assumed to be a widow.
Baptismal dates are often used to approximate birth dates; however, some families wait 3-5 years before baptising children, and adult baptisms are not unknown. In addition, both birth and marriage dates may have been adjusted to cover for pre-wedding pregnancies. It is very common for the first child to be born before or within a few months of a marriage and sometimes baptised in the mother’s name, later adopting the father’s name after the parents’ marriage. The father’s name can be used even if no marriage has occurred.
Calendar changes must also be considered. In 1752 the date of the new year was changed in England and the American Colonies. Before 1752 the new year started on the 25 March, but in 1752 this was changed to the 1 January. This was part of the transition to the Gregorian calendar from the Julian calendar. Many other European countries had already made the change, and by 1751 there was an 11 day discrepancy between the date in England and the date in other European countries. The date continued to be recorded as usual in 1752 until 2 September 1752, the following day became 14 September 1752. Dates that were recorded in the older system can be shown by “double dating”. For example; Original date: 24th of March 1750; Modern date: 24 March 1751; Double dating: 24 March 1750/51.
For events occurring before 1752 in countries where the Julian calendar was still in use, it is best to use double dating whenever the exact year can be ascertained. When transcribing an original record where the exact year is evident but not expressed, the double date can be written as, for example, “24 March 1750[/51]”.
One should also be aware that, in those places using the old Julian calendar, the numbering of months also varied. The “1st month” of the year was considered March, the second April, the third May, and so on. Those 24 days in March which fell before the beginning of the year were generally regarded as being part of the first month.
