If you want to post the actual invoice date from the invoice document the vendor supplied then you will enter it in when posting the invoices in AX. This is helpful for tracking and aging the document. If this is a requirement for you then you probably want to look at the accounts payable parameter require document date on vendor invoice. This can be set at none, warning, error. If set at none a check won’t be done. If set at error then the don’t document won’t post until the date is updated.
This is a quick walk through.