HELP - this one's a doozy

You do NOT change the date. How they enter it is their business, how you record it is your business.

numerical

Personally I would just send them a copy of the original invoice (with the added info) letting them know that their payment is overdue. Let them deal with it on their end. Sounds like they don't want to admit that they dropped the ball and did not pay the invoice. Are there finance charges that should also be added?

If they force you to issue an invoice with today's day I would void the original or issue a credit memo against it and then create new invoice. This will keep both of you happy.

Unless you are on a cash basis, the invoice is last year's income.... last year's date. Voiding or Deleting or changing the date will change last years numbers.

Send them a statement. You did not list the version of QB you have, but in the version I use there is an option "Show invoice item details on statements". Check that box.

The statement will have todays date, and all the information from the invoice.

Although you can issue a credit memo to clear the old invoice, and re-create a new invoice, this would be the last option for me - especially as the client seems to be balking at paying. Original paperwork and pristine records keeping go a long way in court. I would not want to explain to a judge that the guy I was suing had two invoices for the same work with two different dates because *he* wanted it that way.

If there are no late fees involved or any other implications on other transactions between you and the client you could do this:

Bring up the invoice, add the new info and save it.

Bring it up again, change the date, print it before you save it and then click on Revert or Cancel to avoid saving the new date.