Interested in getting feed back on this situation.

I have Invoices that require lots of detailed information and I have invoives that require one line. The invoiced items are not linked back to a product list they are individual and unique. 

I have a staff menber who is not so good with tech and even thow I have tried to make my invoicing as simple as possible she is still getting confused. 

My question is can I have a two Invoice tables , a and b, but have the invoice numbers be incremental regardless of whichever Invoice used. If so how can this be achieved and what sot of scripts would I need. At the moment all of the one lie invoices go to "Shop Sale" and the larger Invoices go to the Customer.

Thanks 

Michael