Let me clarify a few things here. First of all customer has to buy at least 2 X100G ports as a base to start with. Only after that he can buy in increments of 10G. Secondly all consumption based model require smart licensing. So a customer after the initial 2x100G can buy a single 10G out of the 100G, if the traffic goes beyond 10G,no traffic is dropped or port power down. The system will just report the additional usage to the backend Smart licensing server.
The check is done at the backend to see if teh customer has a deficit or surplus of usage/license. AT can then work to get a PO for all teh deficits as true up once a month or qtr depending on their arrangement with the customer.