Tru here.

Some folks get frustrated with genealogy dates listed as more than one year.
I try to use the full dates, as found.
But what causes this “double-dating”?

Julian calendar was used before the Gregorian calendar,
but colonies associated with different countries transferred from the Julian calendar to the Gregorian calendar at different times, with a span of more than 300 years in the transfer.

This creates complication with dating systems.   Found pretty good explanation at ThoughtCo.

Before the adoption of the Gregorian calendar, most countries celebrated the new year on March 25th (the date known as the Annunciation of Mary). The Gregorian calendar changed this date to January 1st (a date associated with the Circumcision of Christ).

Because of this change in the start of the new year, some early records used a special dating technique, known as “double dating,” to mark dates which fell between January 1 and March 25. A date such as 12 Feb 1746/7 would indicate the end of 1746 (Jan 1 – March 24) in the “old style” and the early part of 1747 in the “new style”. Genealogists generally record these “double dates” exactly as found to avoid possible misinterpretation. >> https://www.thoughtco.com/getting-the-date-right-1421812  .

One quarter of my ancestry is from Sweden:

The Swedish calendar (Swedish: Svenska kalendern) or Swedish style (Swedish: Svenska stilen) was a calendar in use in Sweden and its possessions from 1 March 1700 until 30 February 1712 (see below). It was one day ahead of the Julian calendar and ten days behind the Gregorian calendar.  https://en.wikipedia.org/wiki/Swedish_calendar  .

Good explanations
here >> http://www.searchforancestors.com/utility/gregorian.html
here >> https://www.timeanddate.com/calendar/julian-gregorian-switch.html
and here >> https://news.legacyfamilytree.com/legacy_news/2018/07/using-date-standardization-in-genealogy-research.html .

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Family History index at >> https://truthfulkindness.com/about/life-other/family-history-index/  .  Copyright Truthful L. Kindness 05May2020.

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