From the r/StarWars thread:
no, these aren’t negatives. camera negative is generally stored horizontally in separate plastic/aluminum cans within a temperature controlled vault. these are release prints. also, some are listed as being flat (1.85:1) which is either incorrect or some of these are matted prints for certain territories or facilities that couldn’t project anamorphic content.
Another user:
If i had to guess, these would be 16mm reduction prints. Likely for Theatre distribution. A 16mm feature film fits on 3 reels rather than the 6 that 35mm takes up. Also the boxes are the width of 3 16mm reels.
These are definitly not 35mm prints or original negatives.
Those people are right—these aren’t the original negatives, or interpositives or internegatives. These are just used prints.
The original elements for SW are in the salt mines, underground, in a temperature-controlled climate.