"I've almost never heard of Hi Res with a totally new master that wouldn't have been previously available as CD, to be honest. This isn't common, right?"

It has been a few years now since I did all this collecting, but I do remember instances where the CD was brickwalled, but both the Hi Res downloads and the vinyl release got a mastering with more dynamic range.

Well, if you add vinyl, yeah. I had Celtic Frost's Monotheist in that situation, and I bought the horrible CD first.