PS4 shipped 13,5 until end of september right?
Last year PS4 sold to consumers(with supply constraint) 4,2 millions with half november+december.
Lets be conservative and say that PS4 will sell in october the basic 1 million(~1,5 shipped).This puts PS4 at 15 millions shipped at end of october.
and lets be conservative again and say that Ps4 will sell 4,2 millions(november+december) again with supply constraint(sold ~= shipped)
this puts PS4 at ~19,2 millions shipped.
Notice that i'm being way conservative with numbers.
Now i ask you guys,is 20 million shipped at december31 that much far from reality?