Do you not log the training data? Seems like you should be able to just check what was in the training data. To not keep track is just sloppy work and certainly unprofessional science.
That training data does not preserve provenance seems a "smoking gun" in terms of intent to plagiarize.
Does Anthropic, Grok, etc. log their training data? I had the impression it was rather a mess.
The burden of proof is on Buckmaster and Alpöge to reveal if they had the "Improve the model for everyone" setting enabled or disabled. OpenAI shouldn't be expected to reveal private user configuration data. You're asking them to perform a user privacy violation.