I'm surprised to see that the WOWOW and DCP are basically identical. Does the DCP have correctly-proportioned end credits, or are they squeezed like the BD? (When AMC did the 25th anniversary screenings, the credits were squeezed - maybe they just used the BD transfer, like the Cinemark screening of Ghostbusters I went to...)

The Blu-ray transfer may well come from the same element, but it looks to be a different scan - it's slightly zoomed, and seems to be horizontally stretched? (And of course, only the BD has white clipping, crushed blacks, degraining, and edge enhancement.)

And it looks like the BD transfer has red boosting. Marty's jeans already look teal in the WOWOW/DCP (I think this was a bluescreen composite, so that would make sense), but in the BD they look almost green...

The presence of red boosting actually gives credence to your "recycled DVD master" theory. Those transfers were usually done at HD resolution, weren't they? (Though that does beg two questions: 1. Why are the end credits squeezed on the BD and not the DVD? And 2. Why would Universal source from an older, inferior master when they had a different one that was better?)