Let's say we choose 1900 as the cutoff date. That means during training the model is only able to access material written before 1900. It would have a good knowledge about everything discovered in the 19th century and before. There's a great deal of mathematics, physics and chemistry available then. What if now we engage a discussion with that LLM on something discovered after 1900? Say transmutation and nuclear weapons, or general relativity, or the ZFC set theory.