Phil. wrote:

Correct me if I am wrong but wouldn't the 21st century start in 2000.
So there is no need for more than 8 years data to show all of the 21st
century that has occurred so far?

Consider yourself corrected, the 21st century started on Jan 1st 2001.

Given the counting of the millenia are referenced
with the erroneously ascribed birth date of
a delusional popular cult leader,
the precise start dates are not all that significant.