This bit about knowledge cutoff actually is part of the internal pre-prompt which hardcodes September 2021 as a constant (i.e. the service before the AI model itself internally adds "knowledge cutoff: September 2021" to every prompt). So it doesn't say anything about what the real cutoff is. It was discovered months ago when someone managed to make ChatGPT leak the original prompt (and it makes sense: how would the model know about its cutoff otherwise? It's not in the training data). Also we can't tell if it's hallucinating or not when mentioning a different date.