slithy toves

yeah, that's pretty much it is anything that was filmed via telecine technology isn't able to be restored in all of it's amazing beauty cos there are no negatives is my understanding. i'm going to assume you know this more than i do.

oh and yeah, sadly films made before 1952 were filmed on highly flammable nitrate film that eventually turns into a puddle of vinegar. :-( It's by sheer luck that several films still exist. The best looking silent era film I've ever seen is 1929's City Girl. The UK Blu-Ray release is stunning! Ironically while the film exists fully restored, the synchronized soundtrack (on a record) is most likely lost forever.

Yeah slithy there's a limit on status updates

As for Blu-Ray/DVD/film transfers, photographic films has a theoretically infinite resolution. Can push it up to 4K if you wanted. The problem is grain. And whether your views want it cleaning up, or authenticity keeping.