First, to clarify, my approach is very different than Jeff's. If the only
thing (that you need to be able to look back on) that will ever change is
the address, then I think that Jeff's way is better.

Then ther is the low tech way of doing what I was saying, which would be to
print and file the invoice.

To do the electronic way of what I was saying, by software or user
practices, you should make sure that an invoice is treated as a one time
event. After that you are only producing COPIES of the invoice.

Then under my way, you would make an "InvoiceHeader" table which has all of
the "once per invoice" data, exactly as printed. (except for items
mathematically calculated form items on the invoice) mathematically
calculated items) And then the same as the above with an "InvoiceItems"
table.