BTW, fellow pedants
The first year AD (as defined, retrospectively IIRC, and I'm not going to get into Roman/Julian and Gregorian calendars! ) ended on 31 December 0001. Ten years later, the first decade ended on 31 December 0010. Keep going forward in blocks of 10 and the current decade will end on 31 December 2020 (again, happily ignoring the conversion from Roman/Julian to Gregorian calendars
) . We had this debate at the end of the last 'millennium' - the first thousand years ended on 31 December 2000, not 31 December 1999 but there was too much of a party to be had for anyone to really care.
But sure, most people prefer to recognise the end of a decade as 31 December on a '9' year. Decades (brackets of 10 years) of course can end on a '3' year, or any year. We can all have a bit of fun picking the nits. Imagine if
@juddles called the thread 'Happy New Decade!!'
#
# Would have meant no raspberries for him!