I guess when the idea of remastering is called upon, the tracks don’t really require remastering what they require is remixing, a dive into the mix to tweak individual elements however I understand this isn’t possible if the stems ain’t available.
I guess if somebody gave me the job of remastering their master, I have no idea what I’m doing really but have tried my arm at the “Pultec low end trick” a few times , 90% of the time it improves the bottom end whilst clearing mud in the midrange, you can do this with any decent pultec EQ emulation plug-in.