HI again,
We are similar, and I looked for this for a long time. We ended up using the purchase order field for the work date. Shows up on our crystal reports that we give people, but not sure how sortable it is (haven't played with that at all). Some people end up with non-date info in this field. They can see that the invoice date is X (say 6/1/05) and the work date is Y (say 5/3/05) and then they know that the doctor doing the billing was late in turning in an invoice and not that we are double billing. Depending on how you do things, you might also be able to do an invoice number as the date? We use preprinted forms, so need the serially numbered invoice number.
Chris Cripps