The 2.35 number became so popular because it was an atempt to standardize the
anamorphic format (different anamorphic systems have sligtly different ratios), so it
was taken as the ratio of the crop used in cinemas and in DVD transfers.
Cinema projectors allso crop the image a bit with masks.
The image is usually cropped to hide splices if they appear too obvious in the negative.
It allso reduces the "vignette" effect.
I have a scan of the original negative from Alien (1979, panavision gold, same system as SW) right here,
and I have measured the ratio of the original image.
The left edge of the frame (which is reserved for soundtrack) has a slight fade to black rather than
a clear black edge. The actuall image details are visible up to 2.44:1 (after that it is all black, reserved for soundtrack)
But if you cut out the soft fade-to-black edge area (and you have to cut it for transfers) you end up with
2.39:1 which is the real aspect ratio for panavision anamorphic systems.