How to use 3 external monitors on 15" late 2013 MacBook Pro Retina?
3 external displays DOES work. 

I am on a Late 2013 MacBook Pro. I have 1 monitor on the HDMI port, 1 on a displayport to HDMI adapter, and one on an ACTIVE displayport to DVI adapter. I'm thinking that the trick here is to use an Active DVI adapter (mine is from Accell)