How does Net Foreign Assets (NFA) differ from Net Foreign Investment (NCO)?
One is a stock another is a flow.
Net Foreign Assets are:

Net foreign assets (NFA) determines whether a country is a creditor or debtor nation by measuring the difference in its external assets and liabilities. Net foreign assets (NFA) refer to the value of overseas assets owned by a nation, minus the value of its domestic assets that are owned by foreigners, adjusted for changes in valuation and exchange rates.

Net Foreign Investment is:

Foreign investment involves capital flows from one country to another, granting the foreign investors extensive ownership stakes in domestic companies and assets.