After reconciling and validating the invoices, these two documents should be accurate and clean.
When reviewing the income statement for accuracy, consider whether any categories with no/low values are correct. There may be a mistake somewhere.
If any values show dramatically higher than a prior month, consider that as well.
In the balance sheet, ensure that old/erroneous accounts are not popping back in to the balance sheet. This indicates that a recent transaction was coded to an account that may no longer be in use.