Maybe cash flow is not the right term and milestone invoicing fits more here.
We run large projects, some over several years. Some are fixed price others time and materials.
For fixed price projects we usually do milestone invoicing at 30%, 60% and 100% completion of the project.
So we basically need to enter milestones - our future invoices - to be able to predict our income in say 6 months time.
In my understanding this information should be captured in a 'PJC order book' together with details such as sales person, region etc.
It then allows me not only to verify, that the complete order has been invoiced and nothing forgotten, I can also see how much money is likely to come in in the future.