The IID SO 911 can handle more than 999 lines, but because legacy systems such as ACROSS and CCS are still in use, the SO 911 is also limited to 999 invoice lines. Each IID can have a total of 999 invoice lines, so you can report up to 999 CCNs on a single IID, with one invoice per CCN or a combination of multiple CCNs structured into different invoices, but the total invoice lines cannot exceed 999 on any given IID.