Was the Ep.3 Death Star a prototype or was i the same one used in "A New Hope"?
I find it hard to believe that it took about 20 years to build the "ANH" Death Star and it took like 3 yrs, give or take, to built the 2nd Death Star.
It had to have been a 20 yr constrution or a new Death Star after the ep.3 prototype because Tarkin says to Leia aboard the Death Star "Princess Leia, before your execution, i would like you to be my guest at a ceremony, that would make this battlestation operation." Meaning this is it initial use. He also makes this clear when he says: no star system will dare oppose the emperor now. Keyword "now". and when he says "not after we demonstrate the power of this station"
unless the Ep.3 Death Star was completed a short while after the clone wars, but why would the Empire wait more than a decade to only test it much less use it...
The Ep.3 DVD may cover this topic, i'll have to see.