Well-labelled files can make an account review easier without replacing the source records. The first task is to make each file’s meaning clear before joining anything together.
Keep an export register
Use a register with file name, report name, account, marketplace, reporting period, retrieval date and currency. Store the original export alongside it. Put working copies in a separate folder so edits cannot overwrite the evidence.
Amazon’s report documentation lists different fields and availability for different FBA records. Use the definition for the actual report rather than assuming all exports have the same coverage. Amazon’s FBA report catalogue.
Write the matching rule first
Decide how rows relate before merging files. A marketplace and ASIN may identify a product; a seller SKU may be needed to distinguish offers. Check the grain of each file: product, order, transaction or date.
Create a list of unmatched rows. Inspect duplicate keys before adding totals. Repeated ASINs may be legitimate transaction rows, while a repeated product row may indicate that the wrong files were combined.
Hand over a readable working set
The handover should contain the originals, register, matching rule, unmatched-row list and a short note explaining every calculated field. Keep customer contact details out of a general review sheet when product-level totals answer the question. The result is a traceable working set, with missing information visible.