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.
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.