These models will absolutely remember a brilliant insight that appeared a single time in the pretrain corpus, because if they couldn't-- they would get a slightly worse loss. I don't know what this wishy-washing "well maybe we trained on it but we didn't read it" is supposed to mean.
(Example of Fable knowing the content of a deeply unimportant LessWrong post I wrote: https://claude.ai/share/a907b46c-bf7b-4fca-9c71-8582cf8507cc a working Navier Stokes solution would be way more salient)