Blending is where simple one-lot-in, one-lot-out diagrams become misleading. A useful record keeps the documented relationship but does not manufacture precision that the measurements cannot support.
Capture the membership of the blend
Identify the contributing input lots, the operation that combined them and the resulting output lot. Include the declared or measured input amounts and output amount with units and basis. Keep a disputed or estimated amount labelled as such.
Keep the graph conservative
If an upstream input is later found to be affected, the blend output should appear as potentially affected. Where that output is split or transformed again, continue downstream over recorded links. Do not quietly narrow the affected set using an unsupported percentage assumption.
- Document each input
- Show the common process event
- Identify each output
- Flag unknown or unmeasured streams
Use allocation only when independently justified
Physical sampling, process design and accounting methods may support a specific allocation in some settings. Record that as a separate claim with its method, assumptions and review—not as an automatic property of the lineage link.
What this looks like in practice
Lots A and B enter mixer M-7 and produce lot C. A later query about A includes C as potentially affected. If C is divided into C1 and C2, both remain in scope unless reliable process evidence supports a narrower conclusion.
Documented participation in a blend does not prove exact composition or certification of a particular downstream unit.
Primary references
These sources inform the general traceability or due-diligence context. The worked example and operational recommendations above are Atlas editorial guidance.