Regarding whether the negative or a printed positive is used in the optical printer, the original “Star Wars” used black-and-white YCM separations-- also worth noting the YCMs were made on Estar base instead of standard acetate to maximize stability. “Empire” used YCMs as well, but accompanied by a substantially enhanced optical printer with, if I’m interpreting the article correctly, a new lens that finished the composite directly to 4-perf anamorphic rather than on VistaVision where it would then need to be reduction-printed.

The printing tech changed substantially less on “Jedi”, but they made crude black-and-white composites of every VFX shot first (“Empire” only did this for problem shots), which from an editorial standpoint was extremely helpful for the sound team as they could work on these shots before they were finished.

Info comes from https://www.theasc.com/magazine/starwars/ (I’d have preferred direct links but this page doesn’t let me. The articles sourced are Episode IV “Composite and Photographic Optical Effects”, Episode V “Composite Optical Photography”, and Episode VI “Optical Effects”)

Here’s a question: were the original '77 release prints of “Star Wars” made from internegatives? I do wonder how the OCN could be in such notoriously deplorable condition if the numerous prints weren’t made from it (not including the color fading or '97 recuts).