Good methodology cannot fix wrong input.
Use one date
Compare values from a recent point in time. Do not mix current positions with old statements.
Standardize the currency
Convert all amounts at a consistent rate and record the rate used.
Avoid double counting
Check that available funds, principal and interest are not present in more than one category.
Use legal names
For publishers and guarantors, use the legal entity, not just the brand.
Don't fill in the blank
Mark missing information as unknown instead of using optimistic assumption.
Save the primary source
Record whether the value comes from a statement, contract, report or official register.