ANSWER
How do you classify variances during dual-run?
Reviewed .
During dual-run, every variance needs a class before any aggregate match rate is considered: blocker, material difference, cosmetic difference, confirmed legacy defect or approved exception. The record should include the affected rule, evidence, impact, owner, decision and expiry. Without this, a high agreement rate can hide the one difference that prevents cutover.
Step by step
- Link the variance to a rule and fields in the equivalence contract.
- Use blocker when a difference violates a control, critical state, obligation or zero-tolerance limit.
- Separate material differences from accepted format, ordering or rounding variations.
- When the legacy system is wrong, record evidence and explicitly choose not to reproduce the defect.
- Require an owner, rationale, compensating action, expiry and exit condition for exceptions.
How an agent does this
AgenticosCore Parallel produces rule-level diffs and routes blockers and exceptions for approval. House Rules stop progression outside the contract, while Trail preserves the decision for the Evidence Pack.
Frequently asked questions
Can one blocker stop cutover?
Yes, when the contract classifies it as a blocker. The point is to prevent averages from hiding a material violation.
Does a legacy defect count against the replacement?
Not automatically. Evidence and approval determine whether the correct output, rather than the historical defect, becomes the reference.
Primary sources
- AI RMF Core — NIST
- Retiring service components securely — UK Government Security