ChatGPT assures me it doesn't use RAG (fed from my other chat windows), but will use memory-saved preferences (in the store that can be accessed and reviewed in Settings->Personalization->Memory).

Then again, I don't think ChatGPT is reliable when reporting on its own inner workings.

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Oh, no, here it says it also references chat history: https://help.openai.com/en/articles/8590148-memory-faq

You can use ChatGPT for these kinds of questions but it needs to use search or research mode, don't ask it in closed book mode.