Data preparation, without the optimism.

A job starts by establishing what the finished file must be able to do. The file is deduplicated against anything previously supplied to you. If a requirement had no countable equivalent, the nearest one is named.

Size banding

Grouping organisations into ranges that the underlying evidence can actually support.

Legal-entity grouping

Deciding whether branches roll up to one parent or stand alone, and applying it consistently.

Rejection reasons

Every discarded row carries the rule that discarded it, in plain words.

Bring the awkward requirement rather than the easy one; it is more informative.