The boring part, taken seriously.
The first deliverable is a count, not a file. The file is deduplicated against anything previously supplied to you. Each delivery says how old its parts are.
Universe sizing
Establishing how many records satisfy the criteria before anyone decides whether the job is worth running.
Decay review
Identifying the records that have stopped being current, and how many of them there are.
Delivery verification
A final pass against the agreed criteria at the point of handover, not at the point of assembly.
Bring the brief that other suppliers found difficult.