"naturally occurring" means "could be inputs to this AI system from the rest of the world"; naturally occurring inputs don't need to be recognized, they're here as a base case for the induction. Does that make sense?
If there are other really powerful reasoners in the world, then they could produce value-corrupting single pages of text (and I would then worry about Soms becoming corrupted). If there aren't, I'd guess that possible input single pages of text aren't value-corrupting in an hour. (I would certainly want a much better answer than "I guess it's fine" if we were really running something like this.)
To clarify my intent here, I wanted to show a possible structure of an argument that could make us confident that value drift wasn't going to kill us. If you think it's really unlikely that any argument of this inductive form could be run, I'd be interested in that (or if Paul or someone else thought I'm on the wrong track / making some kind of fundamental mistake.)