As to the 70mm cells, I was trying to figure out their origin before, so I analyzed tons of eBay images looking for frames that contained edge codes for print stock and printed in from the previous intermediate generation. Here’s what I found:
SW(ANH) has no printed-in internegative edge codes, and the edge codes on the actual print say EASTMAN LPP and have the symbols corresponding to stock manufactured in 1995. I recently formulated a theory that they had no usable 65mm internegative for the film, the negatives were obviously in dire condition (this was concurrent with the SE restoration), so they simply made a new 65mm blow-up off of a 35mm IB. Do any of you think the SW 70mm cell images look grainier compared to the ESB/ROTJ ones?
Another possibility could be that the internegative had mild fading, I assume the dyes would fade in the same way on negative stock, so you’d be left with a magenta/pink negative image that would turn green when reversed (like that clip on the SE documentary). But it doesn’t look like color information had actually been lost (or not much) just that there’s a green cast.
ESB seems to have been a new print made off a seemingly original 65mm IN. The printed in blue-on-black edge codes have the symbols for 1979, the yellow-brown codes on the very edge on the actual print stock have the symbols for 1995. Some of them look to have shots that were added after the initial 70mm prints (extra Wampa cave, Bacta tank, Falcon dish shown when Luke is hanging on the weathervane thing), so it could have been a slightly later blow-up IN. (I haven’t found one of the extra Rebel fleet shots yet.) But the color looked to have been quite intact at the time - though that was 20 years ago.
ROTJ doesn’t look to have been a new print off of existing internegatives, but rather actual original picture-only (no mag soundtrack striped on) 70mm backup positives? The printed-in internegative edge code symbols are for 1981 or 1982, but the actual print stock edge code symbols aren’t the ones from 1995 like SW/ESB, but instead the ones from 1982 or 1983, depending on the reel. (The cells from the final reel - possibly the final two reels - aren’t faded, and when I found frames showing the print edge codes, they said “EASTMAN LPP” instead of just “EASTMAN”, but they had the symbols for 1982, so they were also original.)