According to Colin Bell, who worked at Technicolor-London on the 1992 restoration of the film with Giuseppe Rotunno, "The Leopard" was photographed in full-frame Technirama (2.25:1 ar), The frame would be trimmed on the left and right sides to an ar of 2.21:1 for 70mm printing, and further cropped at the top of the frame to 2.35:1 for 35mm anamorphic prints. The difference in U.S. and European Technirama specs, which you mention, don't apply here. European filmmakers had adopted U.S. standards by the time "The Leopard" was filmed to accomodate the option of 70mm printing (again, according to Colin Bell).
The image on the Pathe disc is essentially original 2.35:1 (or 2.39:1) theatrical framing with some image trimmed from the top and bottom of the frame. Although it presents more picture info than has been previously seen on DVD, the Pathe doesn’t show “parts of the frame that were not intended to be seen”, as you write. The 2.55:1 ar is, from all I’ve seen, simply the result of less frame height, not additional width. Compare, if you can, the Pathe to the older Medusa or Gaumont DVDs, or Criterion’s disc of the English-dubbed version, and you should see that they all attempt to replicate 2.35 anamorphic framing, some more accurately than others.
The Criterion image is, in my opinion, a rather unorthodox one. It doesn’t replicate intended 2.21:1 theatrical framing as Criterion may want us to think, but rather offers a 2.21 crop of an anamorphic 2.35 image. As was noted when the DVD was released, Criterion chose to trim more image info from the left side of the frame, than from the right, resulting in a somewhat lopsided picture. Occasionally, they decided to scan the 2.35 frame (probably to pick-up action otherwise lost to overscan), and, conversely, cropped more image from the right side, than from the left.
The practices of cropping, panning and scanning are, as Martin Scorsese, Roger Ebert, and other ‘film purists’ have noted, a form of ‘redirecting the film’, and should be avoided when transferring a film to DVD and BluRay. In begrudging fairness to Criterion, occasionally these practices are unavoidable, and, as Criterion claims, Rottunno did approve their work, which I assume includes the reframing. I suppose, in the end, it’s quite similar to, though maybe worse than, Storraro’s reframing of Criterion’s “The Last Emperor". I say 'worse than' because, if for no other reason, Luchino Visconti, unlike Bertolucci, is no longer around to offer his opinion on the matter.
Anyway, I hope this provides a bit of helpful info. Oh, and the Technirama cameras likely came from Technicolor-Rome, not London. Unless they ran short, in which case...
