ISOYEAR (date)
ISOYEAR returns the year of the ISO 8601 week number of date.
An ISO 8601 week starts on Monday. Weeks are numbered from 1. A week including days from two different years is assigned to the year which includes the most days. This means that Dec 31 could be in week 1 of the following year, and Jan 1 could be in week 52 or 53 of the previous year. ISOYEAR returns the year the week is assigned to.
If A1 contains 12/31/2001 then ISOYEAR(A1)=2002