Limit on the number of lines on invoices

Hi. I am working on a business application where products are sold to stores in Japan like MYCAL and JUSCO. The application generates invoices that are then sent with the goods when the stores purchase goods. What I dont understand is the stores Purchase Orders are split up into numtiple orders by the application with a maximum of six lines in each order. This is because the preprinted invoice stationery supplied by the stores has provision only for six lines. This creates 'hundreds' more orders/invoices than is really needed. I would very much appreciate it if someone could explain to me why there is a limit of the numbers of lines on an invoice. I looks to me like every new page has a new invoice number. I want to be able to spread an invoice over many pages. Is this possible. Many thanks to any replies.

Who is making the invoices?
Maybe the system you're using...
Then whether those invoices are for Japan or not, what you should do is to consult with the technical people who supplies or support the system to make the invoices.
They MUST know why they have limitation and may offer you how to deal with it.