It has been in my experience better to keep track of quotes and invoices
separately. Often a customer may argue that a certain prices quoted does
not match what was invoiced, in which case you need to keep track of that.
I would make both a quotes table and an invoice table. You can use the same
form for both and based on how you call the form (like from a menu) base the
record source for the form to the correct table. To simplify creating
invoices off of a quote I would add a button when the form is for a quote
that would copy the data and make the form into an invoice. That way all
the default info will already be entered.
Kelvin