Profiles are saved learner records, not unique people or visits. A shared profile can represent more than one person. Test and imported profiles are included if present. WeChat-linked status reflects the current binding.

First observed means the earliest retained day with a saved response. It is not necessarily a new signup. New profiles use the server record creation date. Total profiles is a current count and does not use the date filter. Returning profiles practiced before the selected period; daily returning counts use each day's own boundary.

Word responses use the larger of saved daily totals and deduplicated response records. Sentence responses count recorded attempts, excluding separate reread events. Finished rounds require an explicit completion marker and recorded practice; stopping early still counts as activity. Counts retain their highest observed daily value when clients prune or replace history.

The daily ledger is backfilled from saved progress and retained weekly evidence. It preserves future observations but cannot reconstruct deleted history. Before collection began, zero means no retained evidence, not proven inactivity. Practice dates follow the app's recorded local day (normally Asia/Shanghai); profile creation and referrals use Asia/Shanghai. Cross-timezone practice is not rebucketed.

Referral metrics count newly identified WeChat accounts acquired in the selected date range, with any qualifying practice by that range's end. They ignore the profile filter. Unidentified arrivals are events, not unique visitors. Website visitor counts, share impressions and visitor-to-signup conversion are unavailable because those events are not collected.