FWIW there were never any official MP4 encodes, but there are re-encodes made by random internet people all over the place, mostly because people really were put off by the file sizes of the official downloads. i.e. if you’re going into this from a film preservation/I want something with better quality than the official releases that I can keep forever, big file sizes aren’t a concern. But if all you want to do it watch a movie once on your phone and be done with it, well, something smaller is probably good enough. Different strokes and all that.

But those MP4s you found might not be a “matched set”, they may be re-encodes made by three entirely different people using entirely different quality/speed trade-offs, they may have made different and possibly bad audio choices, etc. Heck, someone could have spliced Jedi Rocks back into ROTJ for all we know, people do all sorts of weird things. That’s the downside of unofficial sources.