timdiggerm said:

Does it shed new light on the DSII battle?

Not very much. There were some things storyboarded that didn't make the final film, but I think they were all previously known. For instance, when the Rebels realize the Death Star's shield is still up, two fighters can't pull away in time and are flattened against it.

There was also of course initially going to be a greater use of B-wings; storyboards show B-wing pilots as being the ones to destroy the shield towers on the Executor (a quick look at YouTube tells me that A-wings were substituted in the final film).

One thing that did catch my eye, though, was in the Hoth battle. Apparently the Empire was originally going to blanket Hoth with a kind of "electronic net" that prevented ships from leaving the planet. This was the reason the Rebels fire their ion cannon--to disrupt the net and let their transports escape. It was scrapped when ILM couldn't come up with convincing visual effects to pull it off.