The day on which a new year began and the year number increased varied at different times and places during the use of the Gregorian and Julian calendars. For example, England measured the new year as 25 March until 1752, when it switched to 1 January as the new year. In periods of transition, or when writing after a change about dates occurring before a change, it was sometimes common to indicate 2 years with a slash, for example, “30 January 1648/49” meaning “1648 if you count the new year as coming after 30 January, 1649 if you count it as coming before 30 January”. Other notations, such as abbreviations for phrases like “new style” and “old style”, were also sometimes employed.
Many nations transitioned from using the Julian calendar to using the Gregorian calendar. This transition caused a change in dates by several days, which (depending on the date in question) could change the month and year as well. In periods of transition, or when writing after a change about dates occurring before a change, it was sometimes common to indicate 2 dates with slashes, for example “23/6 November/December 1907” meaning “Julian 23 November 1907, Gregorian 6 December 1907”. Other notations, such as abbreviations for phrases like “new style” and “old style”, were also sometimes employed.
Some documents also used slashes to indicate approximate dates, such as writing a birth year as “1903/4” when it was computed from a year-granularity age at a given date.
Versions 5.3 through 5.5.1 had special syntax for recording the first of these 3 concepts with a slash in the year. However, because slashes appear in historical documents with all 3 of the above meanings, some users misused this notation to record the other 2 situations as well. The result is ambiguity in the intended meaning of the resulting data. Version 7.0 removed the year slash notation; a PHRASE substructure should be used instead to clarify meaning.