Can anybody offer some clarity around renewal timings?

I am currently just short of the 24k miles I need (Up to 23/11/2016) to retain Gold, which is obviously my aim. I may have eligible flight(s) before 23/11/2016 which would push me over, or I could buy some tier miles to make it over.

If I buy some tier miles this week, to go over my 24k, does it reset my year i.e. I would be eligible from gold from Aug 2016 - Aug 2017 (which would seem to be detrimental) or does it just add another year on, so gold from Nov 2016 - Nov 2017? In other words, does it matter when you cross the required 24k, in terms of length of gold membership.

Many thanks.