Just looking, 2013 has a spike in bottom Draco numbers compared to 12 and 14,ans it matches the most recent of the (infrequent) bottom Draco fests at bottom-draco (which is not h/d specific, but skews that way)

(09 & 10 are the other years of that fest, and 10 seems to be around the start of the numbers evening out. So I don't know! XD)