what garublador said, when they get to that range for me I dont know that there is any true scientific explanation (pertaining directly to the disc not the thrower) as to why they fly further for me, but I can say that I throw them further. My assumption is that after repeated use the polymer bonds begin to break down slightly before settling into their final state (which probably occurs after a usual disc gets to the 7/10 state) which leaves them more under stable compared to a new one. As a disc becomes more under stable you begin to gain control with it which is where I think the added distance may come from as you can throw it on the best line for max D much easier.
these are all assumptions though other than the fact that I throw my broken in discs further than my new ones in the same mold.