Four-timestamp source tracking model. valid_from (fact became true), valid_until (fact ceased), ingested_at (entered system), invalidated_at (recognized as stale). Implement in CC-DATA-01 engagement records for all corroboration sources. Use for: retroactive forfeiture detection (valid_until < current quarter = expired source), legal defensibility (prove claim timing), longitudinal data quality (track source lifespan). Bi-temporal provenance enables: automatic stale source flagging, entropy rate accuracy, data moat construction. Required for causal modeling. Implement in source database schema.