The above reddit links lists the number of congregations that have apparently been merged.
Summary: 556 congs merged, so 278 congs being closed.
So two congregations are merged into one congregation, therefore one congregation has effectively 'closed'.
Although congregations are merged, other, new congregations may be formed, either in other geographical regions, and/or, in other language groups.
The above reddit chart appears to be based on calender (Jan) years, rather than 'service years' (Sept).
Below is a quick table knocked up to give some comparision of the trend.
Note that the 2006 merged congregation data is from July only. The 2017 merged congregation time period is unknown. The Yearbook data is for the actual year of the book, not the service year (ie 2017 is for 1 Sept 2015 to 31 Aug 2016). I've not double-checked the figures, please let me know if any mistakes!