Well, you may be right but if it wasn't recomposited, something ugly was done when they got rid of the grain...
Technicolor print of the original film
2004 DVD
In the Special Editions, the lightsaber have these ugly sharp edges throughout that actually makes it look rather 2 dimensional, that is not the case with the original. It almost looks like they've digitally erased part of the original animation. What comp mistakes are you talking about?