Protect the source
Retain the original file and record its date and owner. Keep corrections separate from source rows. Comparing unidentified file versions can create false conclusions.
Five essential checks
Check row counts, unique keys and duplicates, date/number types, missing critical fields and totals against the source. Keep the results on a control sheet. Investigate errors instead of hiding them as blank text.
Document the refresh
Document refresh order and reconciliation. Another colleague should reproduce the result using the same steps. Practise this with non-confidential data resembling your work in Excel training.