I don't really thing that its a question if wether the stormstroopers of Episode 4 are the same from episode 2 and 3. A clone really only has about 20-25 years of usefulness, and ten of those years are training. Episode 2 to 4 happened through about a 21 year time frame, which means no the stormtroopers are not the same clone, unless they made new clone, but according to battlefront 2 the kaminos rebeled against the empire so no new clones could be made.
This all explains to me how the stormtroopers lost the ground battle of endor so easily
"Do what must be done, do not hasitate, show no mercy!" ~ Darth Sidious
"Peace is a lie, there is only passion.
Through passion I gain strength.
Through strength I gain power.
Through power I gain victory.
Through victory, my chains are broken.
The Force shall free me." ~ Sith Code