The speaker says that as models improve into mid-training and post-training, the required learning signal is absent from the original data and cannot be recovered by filtering alone.

“and that's quite an automatable process but like as the models get better as we enter mid-training and post-training the signal just like doesn't exist anywhere in the original data we have like no amount of filtering will like get this you know there's no like hidden proof of like the millennium prize problem sitting in common core we can just like”