I haven't received an answer, unfortunately. I have no way of confirming, but I would ASSUME that any log files that contain the data prior to being marked PII will NOT be redacted retroactively. I encourage you to engage your Google account rep if you need a better answer.
Also, note that marking a column as PII doesn't remove its data from the servers--all data for AppSheet apps MUST pass through and be processed by the servers. When marked as PII, AppSheet takes extra steps to reduce the time the data remains on the servers, and obscures the data when presented in administrative tools, all to reduce the availability of the data to Google staff. To the best of my understanding.
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