FOAD is seemingly doing a lot of those retrospectives - Violent Noise Attack, Crawl Noise, Tumor, in addition to the bigger/more well known ones (Rapt, Sore Throat, Regurgitation, Fear of God, 7MON) and I'm hopeful for others like maybe Stench of Corpse, Yesmeansyes, Brutal Glockel Terror....
I'd also like to mention Necrobutcher - NWN did a killer anthology LP a few years back. And those Blood Demos!! Still need to find a copy of the Impulse to Destroy LP.
Stuff like Noise from Brazil has been getting a lot of retrospective attention as well. I bet there are a ton of bands that to some people only existed in the liner notes/thank you lists