Words are something made up to express whatever the speaker/author intends them to, so there is really no such thing as correct or incorrect there. A dictionary can hint at the probability of someone else understanding a word absent of other context, which makes for a useful tool, but that is something quite different to establishing correctness.
As for things that can actually be incorrect, that has always been impossible, but we accept the human consensus to be a close enough approximation. With that, verifying 'correctness' to the degree that is possible is actually quite easy through validating it across many different LLMs trained on the human consensus. They will not all hallucinate identically. If convergence is found, then you have also found the human consensus. That doesn't prove correctness — we have never had a way to do that — but it is equivalent to how we have always dealt with establishing what we believe is correct.