When does a year begin? For some it begins on January 1. But a school year begins usually sometime in September. Fiscal years begin almost anytime. The astronomical year begins at the Vernal Equinox (in March).
A decade, a set of ten years, can begin anytime too. So the first decade of the 2000s ends tonight. And the 201st decade since the time reckoned as the birth of Jesus doesn't end for another year.
ML/NJ
Ohhhhhhhhhhhhhh.....now, you threw a wrench into it.......