iRantanplan said:
Where you are completely wrong however is the BTTF example though. Unforgivable ;)
The wrong cropping in BTTF 2 & 3 came because they took a fullscreen master tape (which already had the cropped wide to full composite scenes) and then cropped it. Of course the framing would be wrong then, it's cropped twice now!
When they fixed it they went back to the original negative and took the original widescreen composite scenes which were matted correctly.

Back to the Future 2 & 3 were both shot open-matte, which means the Fullscreen master isn't Pan & Scan, but rather includes more information at the top and bottom of the screen. You may be right that they cropped the fullscreen master, which in theory would work, except for the fact that open-matte fullscreen releases usually do zoom the slightest bit (and thus lose a little off the left and right, see Waterworld screens earlier in the thread), and the guy who was overseeing the crop must have had his eyes closed.