I've posted elsewhere that I'm quite certain no remixing was done to ESB or RotJ in 1985. Everything about them sounds exactly the same as far as I can tell, based on the samples I've heard.

There may have been a bit of remastering done at some point, as some versions show a bit of peak limiting or slightly more range compared to others, but nothing substantial. I wouldn't even have known it was there without looking at the waveforms.

Changes in mastering level don't make a difference in the scheme of things, since raising or lowering your playback volume will compensate for any discrepancy. No two laserdisc releases seem to have their tracks recorded at the same level; whether analogue or digital, they're all different from each other in that respect.