The table of what midnight UTC means locally makes the bug obvious in a way prose would not: for Los Angeles the daily_key rotates at 4 to 5 pm, right in the middle of an evening session. It is a nice example of a privacy choice (rotating the key daily) quietly becoming a counting choice. Deciding the day boundary once, in one place, also fixes the related reports you mention, not just the visitor count.
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Proof Over Promises.
The table of what midnight UTC means locally makes the bug obvious in a way prose would not: for Los Angeles the daily_key rotates at 4 to 5 pm, right in the middle of an evening session. It is a nice example of a privacy choice (rotating the key daily) quietly becoming a counting choice. Deciding the day boundary once, in one place, also fixes the related reports you mention, not just the visitor count.