Holy dang, y’all! I just managed to clean up 2 years of, what turned out to be, hard water stains!
Thanks to UFYH’s recommendations and lovely tumblr user and fellow unfucker lorimakesquilts (who suggested that it was hard water problems and lo and behold it was). Anyway after the 3rd time of attacking it with strong cleaners and lots of arm strength wielding a hard sponge, that crap is gone!
In fact, the floor is just so dang clean that the “after” photo kept coming out blurry (apparently it’s just THAT clean! that… that’s a thing, right?).