How to recognise COGS when Invoices directly interfaced to AR from external System

Summary:

How to track Deferred COGS and recognise COGS for invoices imported from an external system?

Issue would have been straightforward if Sales Orders were created in Oracle ERP. But if we were to keep Sales Orders outside Oracle, what approach would you reckon to handle the COGS recognition? Would it be a manual adjustments for each external Sales Order that would eventually be recorded as Journals in Oracle ? Or Do you have any ideas?

Edit: Since Sales Order Entry system is external to Oracle, the changes in Oracle inventory owing to shipments will be reflected as a bi-directional sync through Integration