Diesel lubricity additives and many other additives are added in the refinery process and in the tanks at the distribution as needed. The amount added at the distribution centers will vary depending how much fuel was taken out or added from the storage tanks since the last time it received additives. They don't just add a lubricity additives. They also add cold weather, corrosion inhibitors, anti-foam, and many others additives to aid in the transport and storage of fuel. It is kind of hard to move gelled diesel through pipes especially if they are corroded.
Diesel Fuel Additives