unicode date format patterns are a little more nuanced than the “standard”
strftime() supported formats.
note the difference between the following:
man strftime (linux)
%y The year as a decimal number without a century (range 00 to 99). (Calculated from tm_year) %Y The year as a decimal number including the century. (Calculated from tm_year)
man strftime (osx)
%Y is replaced by the year with century as a decimal number. %y is replaced by the year without century as a decimal number (00-99).
and the meaning of
Y in unicode…
Y - Year (in “Week of Year” based calendars). This year designation is used in ISO year-week calendar as defined by ISO 8601, but can be used in non-Gregorian based calendar systems where week date processing is desired. May not always be the same value as calendar year."
turns out that when you’re dealing with a unicode formatting system (and this might not always be obvious) you really need to pay attention to the difference between