This page collects some information on the evolution of the DGS statistics graph here.
This graph is also discussed in this topic.
Nov 2005
OGS born
January 2007 - summer 2010
(to confirm) The number of games had a maximum in 2007 when a special user used to play hundreds of games in parallel. And because of this, there are quotas.
Later followed by a significant downspike?
Dec 2011
Summer 2013
Jan 2015