A requirement arrives in words and leaves as criteria. Each stage writes down what it changed and why. Columns without a written meaning are left out rather than shipped undocumented.
Record identifiers
Giving every row a stable key so a later refresh can be matched against this one.
Entity resolution
Collapsing several records describing one organisation into a single row, with the reasoning kept rather than discarded.
Currency handling
Stating the unit and basis for any monetary field instead of leaving it implied.
We will tell you the ceiling before you commit to anything beneath it.