Record dates prior to September 1752 used the Julian calendar. This tends to confuse researchers when reviewing records produced prior the adoption of the current Gregorian calendar.
The British Empire formally changed systems in September of 1752; the date 2 September was followed by 14 September. To convert Julian dates to Gregorian, add ten (10) days when dealing with the 17th Century, eleven (11) for the 18th.
In addition, the Julian Calendars the New Year began on March 25th not January 1st as the current Gregorian calendar uses. Therefore dates falling between January 1st and March 25th give two years, e.g. 1614/15, which means on that date the year was considered to be still 1614, but by modern accounting it would be 1615.