There would likely be a huge difference between a well stored 16mm o-neg and a rundown print from a flee market. And even if they found a pristine 16mm print, you loose resolution with every copy you make (and I'm sure this effect is magnified by using smaller film) and a print would be at least 4th generation (maybe more for a print for home use).

And how did you figure out the Jabba scene comes from a 16mm copy? I've read they couldn't find the original camera negatives of it but not that the source they used was 16mm and frankly I doubt they could get the quality they did from a 16mm downscale, it was probably some 35mm copy.