The whole decade argument is pointless. People tend to refer to decades as the teens, the twenties, the nineties, etc.... any 10 years is technically a decade as any 100 is a century. So people can count them any way they want, I have gotten over the technical arguments.
2001 technically began the new millennium as 1-2000 comprised the first one. (There was no zero B.C. or A.D.) And so what. We’re about to step out of the “oughties” in a few hours.
So...trying to explain that if the first year of the millenium was considered “0” year, then when going from 1999 to 2000 would have been the new millenium hurt your brain?
In that case (and I agree), they still have another year to wait for the decade that started with the final determination of that election to have passed.