I've taken a shot at "remastering" a couple dozen of the tracks on the music page from about mid-2019 forward. I've never had any formal audio engineering training, so most of what I do is by ear and maybe reading an article here and there. Quite a lot of that doesn't directly apply to my projects because I'm not using the same tools, or throwing heaps of money at the "professional" things the cool kids use.
Although there are a handful of minor changes in some of the mixes (more bass here, less guitar there), for the most part the newer versions just have different "mastering:"" final equalisation, compression, limiting, etc. I finally got a chance to hear to some of them over more-or-less typical music setups and decided many were too boomy and muffled, so I tried to take out some of the mud and brighten them up. I'm still not doing anything sophisticated, but maybe they're a bit better.