What is the primary reason why adjustments to billed invoices are more difficult?

Adjustments to billed invoices are particularly challenging primarily due to the associated payments that have already been applied to those invoices. When an invoice is billed and payment has been recorded, the financial records are impacted by that transaction. This creates a situation where changes to the invoice can potentially lead to discrepancies in accounting, require additional reconciliations, and may affect cash flow reporting. Adjusting the invoice means also considering the impact on payment records, ensuring that the correct amount is reflected across all related accounts. This linkage can complicate adjustments because any change needs to be seamlessly integrated into the overall financial system without causing inconsistencies or errors in the account balances.

While it is true that invoices may be finalized, or might not be modifiable in some systems, the primary complexity arises from the payments which must be tracked and managed alongside any adjustments to the amounts billed.