Well, if they hadn’t abandoned the old EU (which they hadn’t when they made Ep III), then the death star we see in Ep III is the prototype (http://starwars.wikia.com/wiki/Death_Star_prototype), not the Ep IV Death Star. I would say that its appearance in Ep III after its creation in the EU makes the prototype version canon, though it isn’t specified. It just doesn’t make sense otherwise. Why take 20 years to build the first one and 4 to build the second. First spend time on the prototype, make sure the parts work, then build the first death star and maybe spend 5-10 years to build it. After 4 the Second Death Star was incomplete, not having shields and likely not propulsion, but an active reactor and super laser. Still a long way from completion.