Just from Attack of the Clones, most of what had specifically happened is left to your own imagination - all that is clear to the audience is that Cloners have been paid to build an army for the heroes but that it is really the villains that have had a hand in it. In other words the idea that this army is too good to be true and is going to have massive implications in the future is there and is really all that is necessary. Sure there is enough there to make suggestions and implications about how it happened - in many ways that is in all of the films from A New Hope on - but the film provides enough. I didn't need to know how the Rebels got hold of the Death Star plans, how the Empire managed to build it, how the Rebels managed to keep their entire organisation secret on Hoth for a time, where is the Emperor for two films etc.