Duplicates, orphans, format chaos, and fields repurposed by folklore — the audit that sizes cleansing effort and prevents the schedule from being fiction.
Field-by-field source-to-target with transformation rules, signed by the business owners who know what 'customer type 7' meant in 2016 — assumptions here become production incidents later.
Full dry runs on production-scale copies: duration measured, errors triaged, reconciliation counts (records, sums, balances) proven — the rehearsal is the confidence.
Freeze windows, checkpointed runbooks, rollback criteria decided in daylight, and parallel-run verification after — migration discipline is rehearsed choreography, not a long night of hope.
Skipping the discipline this article describes until an incident, audit, or stalled project forces it — every practice above is cheaper adopted early than retrofitted under pressure.
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