Are you trying to help, or just see how confused you can get everyone???

"Year 1 to end of year 1000 is 99 years (there was no year zero)"

There was no year zero. but... from the beginning of year 1 to the end of year 1000 was 1000 years. Not 99. Not 999. What are you saying?

"Year 1000 to end of year 1001 is one year.... equals 1st millennium"

One year does not equal 1st millennium. From start of year 1000 to end of year 1001 is 2 years - the last year of the first millennium and the first year of the second millennium. What equals 1st millennium?

"Year 1001 to end of year 2000 is 99 years (count them if you don't believe it)"

You count them. Are you including year 1001 or not? Where do you get 99?

"Year 2000 to end of year 2001 is one year .... equals 2nd millennium"

Which year?

"January 1, 2001 is the first day of the beginning of the 3rd millennium."

TRUE!!! (But the road you took to get there... sheesh!)