HKT windows and deploy markers
Sprint KPIs and error budgets can move when clocks and deploy tags move—not when the product does.
Teams serving users in Hong Kong often mix UTC warehouse timestamps with HKT engineering calendars. A cohort day that spans the wrong midnight shifts every retention and throughput cell without anyone shipping a feature.
Missing or duplicated deploy markers create similar ghosts: returning users appear as new cohorts, and day-seven rates look healthier or worse depending on merge rules.
Before celebrating a KPI lift after a platform migration, list SDK versions, identity rules, timezone settings, and deploy tags beside the chart. If those moved, treat the chart as suspect until you rebuild from raw events.