ADD_YEARStakes a date, from either an information or in ISO8601 format, and a number of years to add, and returns a date with the given number of years added.
In the special case that the new year doesn't contain the original date (e.g. when adding a year to the leap day 29.02.2016) the new date will have the same number of days from the beginning of the year (e.g. 01.03.2017 in the earlier example).
2018-01-01T00:00:00, so the year 18 years after the 1st January 2000.
If you specify not just a date, but a date and time in ISO8601 format, the function includes the time in the calculation.
This returns also the 1st January 2018, but at 9:35:23, so