When working with invoices in artcloud, you'll notice there are two date fields:
You can override either of those dates for a given invoice.
When creating a new invoice, the date field will automatically show the current date. To change the date, click on the date field and select the correct month, day, and year.
Once the invoice has been paid in full, a new date field will be displayed on the invoice: Closed Date. You can override this date in the same way.