Answer: name the materials in the contract and make each lot produce a value you can compare — substitution hides in the gap between "same spec" and "same material".
- Contract — conductor grade, plating, jacket compound, E-Marker IC and shielding construction, by name.
- Measurable checks — conductor resistance, weight per metre, plating thickness, E-Marker read-out.
- Per-lot records — the values must be recorded per lot, not once at approval.
- Change control — any material change requires written notice and re-approval.
Weight and resistance are cheap to measure and hard to fake at scale.