Legal wants written confirmation that no customer PII r...

Providing a blanket certification that no PII exists in a pre-training corpus is technically impossible because the tokenization process erases document identity, making it impossible to enumerate or audit specific source documents.

Instead of a binary confirmation, you should provide a rigorous statistical measurement. Explain the sample-size arithmetic used to audit the data and the confidence intervals this provides. Finally, define the remaining risk in terms of extractability, which is a more accurate and defensible way to characterize privacy risks in large-scale machine learning models.