Not sure if this helps, but you can probably get the information from the SO_SalesOrderHistoryHeader file.  This file should have an invoice number field.  It will be blank if an invoice has not been created.

No, unfortunately that doesn't help. I don't need the invoice number, I need a constant value of Y or maybe like the date the invoice was created.

Nevermind, I figured it out.

Nevermind, no I didn't

If you want to translate this field value into a Y/N UDF, you'd need a script.

You can also check the OrderType field in SO header.  S = no invoice.  B = at least one invoice.

That Last Invoice Date field would work. How did you get that populated?

Our OrderType field never changes. It's always Standard.

Go into SO Invoice Entry, create a new invoice, and enter the SO # (before leaving the Header tab).  Set line quantities, post, and the SO is updated then with what was invoiced (but if all lines were shipped complete, the SO disappears from SO Entry).  If any lines were short-shipped, the OrderType changes to B, with a Last Invoice No populated and line quantities updated.

Retaining SO history is optional, and if you need to report on fully shipped SO, you will want to ensure that is turned on.

Oh, we create all orders in Sales Order Entry. I guess that's why those fields don't work? And the order type never changes?