And OpenAI say that they use the prompt to improve the model:
> When you use our non-API consumer services ChatGPT or DALL-E, we may use the data you provide us to improve our models. You can request to opt-out of having your data used to improve our non-API services ....
Don't you love the beauty of opt-out Data Collection?
And they also warn to not use sensitive information in the prompts:
>Q: Who can view my conversations?
A: As part of our commitment to safe and responsible AI, we review conversations to improve our systems and to ensure the content complies with our policies and safety requirements.
>Q: Will you use my conversations for training?
A: Yes. Your conversations may be reviewed by our AI trainers to improve our systems.
>Q:Can you delete specific prompts?
A: No, we are not able to delete specific prompts from your history. Please don't share any sensitive information in your conversations.
That's not true. It uses reinforcement learning from user interactions and therefore the content of those conversations becomes part of the model. The 2021 cut-off was once true but it's obvious the GPT has knowledge beyond that. You can test it yourself using many of the prompt manipulations and press the AI to discuss factual events after that date. It seems that the only reason it will refuse to normally speak about stuff after that date is that it's restricted by the guards OpenAI have put in place.