My understanding about the date of training from ChatGPT page: ChatGPT is fine-tuned from a model in the GPT-3.5 series, which finished training in early 2022. So it was based on a model from early 2022 but it was partially trained (fine-tuned) and published in November 30, 2022. But I can't find conclusive evidence about the exact date. I hope if an OpenAI engineer would enlighten me ...